Processing of Barley

Introduction

            Barley is one of the world’s oldest domesticated crops and competes with wheat for the honor of being the first wild plant form through under cultivation. Barley (Hordeum vulgare) is the world’s fourth most important cereal after wheat, rice and maize.

            Barley is one excellent source of B-complex vitamins and minerals. Like other cereals, barley is also considered nutritionally poor due to low content of essential amino acids like lysine and threonine. However, breeders have discovered high lysine barley genotypes, which indicate the scope of nutritional improvement in this crop.

            Barley genotypes have been classified as hull less and hulled ones. Barley and oats are unique among cereals, containing relatively high concentration of the mixed linked (1-3), (1-4), b-D glucans (b-glucans). Hulled barley contains 3-7 per cent b glucans while hull less may have as much as 16 per cent b-glucans.

Classification

• Genus - Hordeum
• Tribe - Triticeae
• Subfamily- Festucoidese
• Family - Gramineae      

Barley is a grass of the family Gramineae, subfamily Festucoideae, tribe Triticeae and genus Hordeum. 

Structure

a.   Plant :  Barley has overlapping auricles compared to wheat (smaller non-overlapping auricle) and oats (rudimentary auricles), which are readily distinguished at the seedling stage.

b.  Spike : The spike is made up of spikelets with three florets attached to each of the nodes of the rachis. Two sowed barleys have one, fertile florets, whereas six sowed barley have three. The flowers are arranged in spikelets on the head and are attached at nodes of central stem. The spikelet is composed of the male and female flower parts enclosed within the lemma and palea. The rochilla is attached to the germ end of the kernel and lies in the furrow of the palea.

c.  Kernel : The mature kernel is composed of the hulls (lemma and plea) enclosing the caryopsis and of the rachilla. In most varieties, the hulls are cemented to the caryopsis and make up a part of the threshed kernel.       

In nobed or hull less barleys, the kernel threshes free as it does in wheat. The kernel dry weight is made up of approximately the following percentages of tissue; husk and pericarp 10% aburone and associated testa pigment strands and some nuclear tissue, 14%, starchy endosperm and nuclear remains in sheaf cell region, 73%, embryo, 3%.

Classification of Cultivated Species :

            Plants of the genus Hordeum of the grass family Gramineae, have simple species. The cultivated types of barley and the two most closely related wild forms are included in the section Cerealia. Wiebe and Reid (1961) classified cultivated barleys into three species on the basis of brittleness of the rachis and number of kernel rows on the spike. They also gave detailed descriptions of taxonomic characteristic for growth characteristics of varieties commonly grown at the time.

            Most of the cultivated barley have been classified into the two groups, H. vulgare L., the six sowed barleys, and H. distichum L., the two sowed types.

Two Sowed Types (Hordeum spontaneum C. Koch, Hordeum agriocrithon Aberg) : It was considered to be the progenitor of cultivated six row barleys. This barley has a tough rachis and is not found in the wild away from areas of cultivated barleys. In the common two-rowed group, the lateral florets are sterile and greatly reduced. Only, one row of kernels develops on each side of the spikes. The kernels are all symmetrical and more uniform in size than the six-row barley, but the kernels that develop at the base and at the tip of the spike are often somewhat smaller than those in the center.

Two Rowed Barleys : Three kernels develop at each rachis node. The median kernel is slightly larger than the lateral kernels on each side and is symmetrical in shape. The two lateral kernels are twisted and the twist is more pronounced at the attachment end of the kernels.

Production of Barley :

            The world area under barley cultivation has been steadily increasing. The production increased from 83 million tones in 1961-62 to 132 million tones in 1971-72 and to 162 million tones in 1980. The chief barley producing countries in the world are the USSR, USA and Canada.

            In India, barley is grown mostly in the northern part of the country. The area under cultivation was 0.72 million hectares in 1951-52 which rose to 1.75 million hectares in 1980, which a production of 1.6 million tones. The yield is the order of 7.5 to 9.0 quintals per hectares as against a world average of 19.5.  In India, production is largely confined to Utter Pradesh, Punjab and Haryana but however it can be grown anywhere the wheat can be. In Haryana, barley crops cover 58000 hectares of land area and total yield is 160,000 tonnes.

Chemical Composition of Barley :

            Barley grain is rich in starch and sugars relatively poor in protein, and every low in fate. The husk (lemma and palea) is mostly composed of lignin, pentosans, mannan, uronic acids, hemicelluloses and cellulose fibres. Silica is present in the outer walls of the husk and the awns contain large amounts of silica. The paricarp lacks lignin. The testa contains crude cellulose and pigment strands of alpha waxes, which are a barrier for chemical substances and microbes polyphenols which may complex with proteins are abundantly in the pericarp, testa and aleurone layer. The aleurone has thick cell walls composed of arabinoxylans and has aleurone grains of protein and phytic acid, pherosomes rich in fat and abundant minerals. The subaleurone layer of the endosperm is composed of about 8.5-8.9% starch enclosed in cell walls. b-glucans make up 75% of the cell wall and the rest is arabinonxylons. The embryo consists of about 7% cellulose, 14-17% lipids, 14-15 % sucrose, 5-10 % raffinose, 5-10% ash and 34% protein. The cell wall of the embryo contains uronic acids, pectin and hemicellulose.

A. Carbohydrates

(i) Starch : Starch is a polysaccharide, µ-glucan, and can be divided into straight chain amylose and branched chain amylopectin. The starch granules in the barley endosperm are laid down within amyloplasts and fall into two size groups 1.7-2.5mm and 22.5-47.5mm. These starch grains contain traces of lipids, minerals, proteins and nucleotides. The starch is synthesized in plastids. The “disatatie” enzymes responsible for degrading the starch in germination are phosphorylase, µ-glucosidase, µ-amylase, b-amylase, debranching enzymes and transglucosylase. In normal barleys the ratio of amylose to amylopectin is about 1:3, in high amylose glacier about 1:1, and waxy barley is 97-100% amylopectin.

            Barley starch has A and B granules similar to those making up wheat starch. The smallest granules (<2.7 microns) constitute about 74% of the total, the largest (>13.6 microns) about 9.4% and those of intermediate size about 16.6%. The larger starch granules of barley have a higher amylopectin percentage and a lower gelatinization temperature than the smaller granules.

(ii)  Soluble Sugars : Glucose and fructose are found free and in combination, whereas other monosaccharide are polymerized as oligosaccharides, polysaccharides, glycosides, glycolipids and glycoproteins. Soluble sugar content of normal barley is about 2-3%, hullless barleys 2-4%, high lysine barleys 2-6% and high sugar barleys 7-13%. The total sugars and reducing sugars declines from anthesis to maturity, whereas non reducing sugars are constant in amount during plant growth. The major sugar of living tissues of barley is sucrose.

(iii) Non Starch Polysaccharides : Briggs defines these polysaccharides in barley as ‘pectin fractions’ or Hemicellulosic materials, which are then divided into gums of soluble in hot water and hemicellulose if soluble in alkali. The material removing after delignification and removal of gums are ‘hemicellulose’. Endosperm gums consists of b-glucan and an arabinoxylan. Barley, like oats has a relatively high b-glucan content and barley cultivars of the waxy starch type consistently have greater b-glucan concentration (about 50 % more than standard barleys). Some of the b-glucan of very large molecular weight are not water extractable and cannot be considered gums, though they are part of the dietary fiber content. The small amount of cellulose which is present in the grain (about 4 to 5%) is located mainly in the cell walls of the aleurone-testa tissues. Fructosans can be detected during the ripening of barley, the final level being about 0.5 to 1%.

B. Protein :

            The two major groups of storage proteins in barley are the glutelins and the protamines, present at levels of around 4% each, with somewhat more glutelin than protamine (hordein). The limiting amino acids in barley protein are lysine followed by methionine, threonine, and tryptophan. In barley, the albumins and globulins (soft soluble) which are rich in lysine (5-7%) and threonine, are mainly metabolic proteins. The prolamines are the major shortage proteins of the endosperm and are low in lysine (<2%). The glutelins also found in the endosperm, are associated with found structural proteins of the membranes and are about 4% lysine. Some protamines (hordien) are also present in the protein, bodies of the aleurone cells. The albumins and globulins include the enzymes, they are found mainly in the embryo and aleurone.

            The content of peptides and free amino acids in ungerminated barley is low, normally less than 0.2% of the grain.

•             Albumin - 10%
•             Globulin - 20%
•             Hordeins  - 30%
•             Glutelins  - 40%

C. Lipids :

            Barley lipids content is low (2-3%) compared to maize and oats. Tryglycerides comprising 77.9% of barley lipids contain palmitic acid and the unsaturated fatty acids, oleic, linoleic (principle one of barley kernel) and linolenic. The barley kernel also contains diglycerides, free sterols, free fatty acids and sterol, esters and hydrocarbons. Most of the lipids are in the endosperm (77%), embryo (18%) and hull (5%). The fat content of a developing plant increased and then may decrease slightly. About 78.2% of the total is neutral lipid, 7.3% glycolipid and 14.5% phospholipids. The fat content of normal covered, normal hull-less, high sugar and high lysine barley range in percentage from 1.9 to 2.4, 2.4 to 3.9 and 4.4 to 7.3 and 2.9 to 5.8, respectively. Low levels of waxes, free sterols alkyl resorcinol, carotenoids, nonthophylls, and tocopherols have been reported. Over 4% of total lipid occurs as linolenic acid. Less than about 1% of stearic, palmitoleic and myristic are typically present.

D. Vitamins :

            Barley is and excellent source of the vitamins thiamine (B₁), pyridoxine (B₆), riboflavin (B₂) and pantothenic acid. It is also quite high in niacin. Vitamin E is present in the as a mixture of tocopherols which is present found at levels of about 6 to 45 mg per gram of oil. Some biotin and folacin are also present but carotenes or vitamin A, B₁₂ or D are found in ungerminated grains. The description of vitamin contents are as follow:

•             Choline :    0.9 to 2.2 mg
•             Thiamine :   1 to 16 mg
•             Riboflavin :   0.8 to 3.7 mg
•             Nicotinic Acid :  47 to 147 mg
•             Pentothenic :  3.7 to 4.4 mg

            (As Calcium Salt)

•             Biotin : 0.05 to 0.1 mg
•             Inositol : 1.4 to 3.2 mg
•             Pyridoxin : 2.7 to 11 mg

            Embryo scutellum and aleurone contain more vitamins than the other tissues.

E. Minerals :     

            The distribution of minerals is uneven throughout the kernel and the rachis (5-14%) and owns (17-38%) contain a large portion of the minerals. The ash content of barley ranges from 2.2 to 3.9%. The phytic/nonphytic phosphorus ratio of barley was about 2 in barley compared to 3 in wheat and oat and 13 in rye. These ratios are meaningful because phytic acid decreases the availability of certain minerals. In the whole kernel of barley the minerals present in greatest amount are phosphorus (2.97 g/kg), potassium (4.39 g/kg) and magnesium (1.29 g/kg). Calcium and sodium are found in much lower levels 0.257 and 0.138 g/kg, respectively. Still lower, but significant quantities of iron, zinc, magnesium, and aluminum are present 28, 23 and 10 micrograms per kg, respectively. Traces of copper and molybdenum can found.

F. Phenolic Compounds :

            In plants the phenolic compounds can be divided into benzoic acids, cinnamic acids, terpenoids, and flavonoids. Barley contain a wide range of phenolic compounds in one form or another ranging from free and combined tyrosine, tyramine and derivatives, phenolic acids, esters and glycosides and numerous other phenols though lignons and substance related to lignons. Phenolic compounds may also inhibit nutrient utilization.

Milling of Barley

            Barley is millet to make blocked barley, pearl barley, barley grots, barley flakes and barley flour for human consumption. Removal of the hull or husk of barley, which is largely indigestible is and important part of the milling process.

Intrinsic qualities : The milling is done in barley to achieve :

1.      Absence of sprouting.

2.      Absence of discolouration due to weathering.

3.      Freedom from fungal attack and insect infestation or damage.

4.      Soundness of appearance.

5.      Absence of undesirable aroma or flavour.

The harder types of barley is best for milling purposes because the hull and bran can easily be removed from endosperm by superficial abrasion and yielding particle will retain the shape of the whole grain. The softer grains are not better because they would tend to fragments, leading to a reduction in the yield of first quality products.

            Barley for milling should have as low as hull intent as possible. The presence of damaged grains lowers the quality of milling barley. Such grains frequently reveal areas of exposed endosperm where fungal attack may occur leading to discolouration and intrigues discoloured particles to the finished products. Thin grains also lower the milling quality with a higher hull content than normal they make a small contribution to the yield of milled products.

Operations : the sequence of operations in barley milling may be summarized as follows.

1. Preliminary Cleaning : Barley is cleaned on machines similar to those used for wheat cleaning, viz. milling separators, drier cylinders or indented dishes, and aspirators. The sizes of sieve aspirators and indents are modified for the comparatively larger size of barley grains.

2.   Conditioning : Conditioning consists in adjustment of moisture content to about 15% by drying or damping and resting for 24 hour.

3. Bleaching : Barley is used to bleach with moisture and sulphur  dioxide. Blocked barley is fed into a vertical earthenware cylinder. Into which steam and sulphur dioxide are injected. The quantities used are 1-2% of moisture and about 0.04% of sulphur dioxide and solution of sulphurous acid (H₂SO₃) or of sodium disulphide (NaHSO₃) can be. The treatment take about 20-30 min time, after that the barley is binned for 12-24 hour for the bleaching to take effect. Excessive quantities of sulphur residues in the final product should be avoided.

4. Blocking and Pealing : Both blocking and pearling of barley are abrasive scouring processes differing from each other merely in degree of removal of the superficial layers of the grain batch machines or the rate of throughput  in continuous working machine.

5.  Aspiration : Aspiration of the pearled grain to removes the abraded portions and cutting of blocked barley into portions known as grits and it is similar to those methods done for aspiration of oatmeal. In Germany, the blocked barley is first cut into grits, the grits graded by size and then sounded in the pearling machine.

6. Polishing : The pearl barley is polished on machines similar to those used for pearling but equipped with stones made of hard white sandstone instead of emery composition. The average yield of barley is 67% of the whole barley.

7. Steam Cooking and Flaking : Barley flakes are made from pearl barley by steaming and flaking on large diameter smooth rolls.

8. Drying : The flakes are dried to about 10.5% moisture content before packing. Barley flakes are made from pearled barley has been used as flavouring ingredients in specially breads in the USA.

            Pearl barley is used for sups and dressings and for the manufacture of puffed barley, a read to eat breakfast cereal. Pearl barley blocking removes part of the husk, this process must be accomplished with the minimum of injury to the kernels. The pearling carried out in two stages, removes the remainder of the husk and part of the endosperm. The three processes remove about 5%, 15% and 11%, respectively to yield a final product representing about 67% of the grain.

Three types of blocking and pearling machine are in general use :

(i) A fetch machine consisting of a large circular stone, faced with energy cements composition and rotating on a horizontal axis within a perforated metal cage.

(ii) A continuous working machine consisting of a rotator faced with absorsive material rotating on a horizontal axis within a semicircular stator lined with the same material, the distance between rotor and stator being adjustable.

(iii) A continuous working machine comprising a pile of small circular stones rotating on a vertical axis within a metal sleeve. The annular space between the stones and the sleeve occupied by the barley being strongly aspirated. The barley bolls between the rotator and the stationary part of each machine in bouncing from one surface to the other the husk is split or subbed off. The degree of treatments is governed by the abrasiveness of the stone flung by the distance between rotor, and station and by the time of treatment in is also a starting material for the manufacture of barley flour. Milled barley are also used for extruded food snacks as croutons and salad dressing as crunches for nut substitutes.

Barley Flour

            Barley flour is milled from pearl barley, blocked barley or unpearled hull less barley. Optimum tempering conditions are 13% moisture content for 48 hour for pearl barley, 14% moisture content for 48 hour for unpearled hull less barley. The milling system uses solar mills with blunted and smooth rolls and plansitfers.

            When blocked barley or whole barley is used for milling barley flour, due allowance must be made for the greatly increased quantity of by products, which would otherwise hope the system. Barley flour is also a by products of the cutting, pearling and polishing processes. 

                     

Barley Types	Extraction Rate
Pearl barley	82%
Original whole grain	55%
Blocked barley	59%

            

A blend of hull less barley and wheat can also be milled at the ratio of 10:90 to 20:80. When barley flour was blended with wheat flour in ratio of 10:90 to 30:70, bread characteristics were better with hull less barley flour than with hulled barley flour, but bread quality deteriorated as proportion of barley flour increased.

            Barley flour is used in the manufacture of flat bread for infant food and for food specialties. It is also a component of composite flours used for making yeast raised bread.

            Pre gelatinized barley flour which has high absorbent properties provides a good binder and thickener. Combining pre gelatinized barley flour with barley crunch makes barley breading.

            The coarse by products from the blocking process are fragmented on a chamber mill and the ground product combined with the residues from the two peeling operations for use as animal feed.

Malted Barley Flour

            Barley malt is ground or milled to make malted barley flour. Malt flour is used as a high diastatic supplement for bread flours, which are low in materials diastatic activity, as a flavour supplement in malt loaves and for various other food products.

Air Classification : Malted barley flour can be our classified to yield protein rich and protein poor fractions. The former used in the food industry, while the later is used to make unique beer.

            Other products derived from malt include kibbled malt, malt extract and cereal syrups. The major food uses for malt products and cereal syrups are in bread, biscuits, crackers, crisp breads, breakfast cereals, infant and invalid foods, matted food drinks, pickles and sauces, sugar confectionary and vinegar.

Molting

            Molting is a controlled natural process rather than a manufacturing operation. Essentially barley kernels are allowed to grow under precisely defined conditions in order to bring about specific, desirable changes in the physical and chemical properties of the kernel. Growth is then stopped by removal of water. Flavour components are developed by gently heating and curing the malt.

            Finished malt resembles barley, but only superficially. Within the kernel, natural enzymes formed and stimulated by controlled moisture, aeration and temperature have:

1.      Broken down cell wall material in the endosperm,

2.      Rendered some of the protein soluble in water,

3.      Started to degrade some of the starch granules fermentable sugars.

Barley is cleaned, sized, segregated by variety and protein content and stored for several months to break any dormancy. The amount of water-soluble extract obtained from malt is dependent to a large extent on the amount of starch in the kernel. From this extract, brewers produce beer. Low protein (13% dry basis or lower), plump kernels have a higher proportion of starch and other factors being equal produce a higher quality brewer’s malt.

The following steps are involved :-

1.   Cleaning and Grading : On intake, barley is cleaned to remove dust, chaff, weed seeds, thin barley and other grains. Cleaned barley is graded according to size plump and medium grades of barley, retained in sieves with slots 2.5, 2.4, 2.2 and 2.0 mm wide or 2.2 mm sieve is too thin for malting and is sold as feed.

2. Steeping : Growth is initiated by the absorption of water into the kernel in conical bottomed steep tanks. Water at 12-16⁰C and air, respectively are provided to barley over a period of 40-48 hour. Water enters the embryo through the micropyle, a small opening, until the moisture content of the kernels rises to 44 to 46%. The water is changed every 6-8 hour and is never recycled. Molt houses create a significant volume of effluent with a high BOD. Compressed air bubbled through the steep agitates the barley to ensure all surfaces are washed.

Gibberellins, plant hormones, are synthesized by the embryo and diffuse to the aleurone layer of the barley kernel. Here they stimulate the production of the hydrolytic enzymes capable of degrading barley starch granules, protein and nucleic acids. Enzyme production also takes place in the embryo.

Later aerations remove the carbon dioxide from as a respiratory product of initial growth

3.   Germination : From the steep tank, the barley falls by gravity or is gently conveyed to the germination vessel. Over a period of four days at 13-16⁰C and 100% humidity the barley grows. The bed is gently turned by machine to prevent the soot lets from malting and to promote uniform growth throughout the bed. Using large volumes of air and water sprays, the temperature is controlled and carbon dioxide removed. Germination is considered complete when the endosperm is fully modified which means:

(i)  The cell walls are largely dissolved to expose the starchy interiors of the cells.

(ii)  Those catabolic enzymes are formed which will convert high molecular weight carbohydrates to low molecular weight carbohydrates and sugars.

(iii) Degradation of some proteins to soluble peptides has begun. These peptides will nourish yeast in the fermentation process; some will remain in the finished beer giving it mouth feed and tenure. Fully germinated barley is called green malt. Germination is carried out in drums on rotating floors, in salad in boxes or the wonder houfen system 

4. Kilning : Kilning can be carried out in the same vessel as germination. To save energy, kilns are often arranged on two levels, one directly above the other. Initiate drying takes place in the upper kiln, using the residual moisture removing capacity in the warm air coming from the lower kiln. Air fully laden with moisture is then exhausted to the atmosphere.

To prevent denaturation of the enzymes required by the brewing process, green molt is gently dried. The drying air temperature is increased from 50⁰C through various levels to a final temperature around 80⁰C. Air forced through the fed gradually lowered the moisture content of the malt to 4%.

Later stages of kilning are referred to as the curing process, during which most of the flavour components of malt are generated. These are predominantly heat induced chemical compounds called maillard reaction products; they characteristically develop when amino acids and sugars are heated together. Following kilning the brittle rootlets are easily removed and role as a high protein (75% dry basis) feeds supplement for livestock.

The malt is stored, often for reversal weeks to regain homogeneity and equilibrium, prior to blending and shipment.

The yield of malt from barley is about 75% some typical losses consist of:

• Cleanout from raw barley - 7-9%
• Respiration during steeping and germination - 4-5%.
• Drying (barley, 13.3%, malt 4%) -  9-10%
• Malt rootlets and hulls - 3-4%

5.  Malt Analysis and Shipment :  Control of all aspects of the steeping, germinating, and kilning process must be reliable and precise. Variances as small as 1% in the moisture level or 1⁰C in the temperature have a significant effect on the analytical values of the final malt.

Use of Malt : Special malts such as caramel, black, amber roasted, and Munich malts impart colour and additive flavour to beer. They are produced by various degrees of roasting, to the concomitant detriment of the enzymes. Peat malt has the savor of peat smokes. Crystal malt is green malt rapidly heated. The interior is glassy and the taste is luscious.

            Distiller’s malt with its high enzyme activity and less emphasis on flavour is produced by kilning at low temperatures. Hopped malt extracts are used in specially breweries and home brewing kits.

Other uses for malt are in baking, confectionary and breakfast foods.

Antimicrobial and Their Application in Foods

Antimicrobials will undoubtedly continue to be needed to provide the food supply that will be demanded in the future. The global economy in which we live will result will be demanded in the future. The global economy in which we live will result in foods being transported throughout the world. If foods are arriving in the condition expected, preservatives will be needed. Many chemical compound, either present naturally or formed during processing or legally added as ingredients, are capable of killing microorganisms or controlling their growth in foods. They are designated as antimicrobial inhibitors. A preservative is defined as any substance, which is capable of inhibiting, retarding, or arresting the growth of microorganism, of any deterioration of food due to microorganism or of masking the evidence of any such deterioration. Antimicrobial compound add to products during manufacturing process to reduce bacterial or fungal growth. 

According to PFA Act, (1951)

      A substance which when added to food is a capable of inhibiting, retarding, or arresting the process of fermentation, acidification or other decomposition of food.

    Antimicrobial food additives are

Ø              An efficient

Ø              Cost effective

Ø              Only effective way to control fungal growth in foods.

Occurrence

Ø              Naturally occurring in certain foods

Ø              Added to foods during processing.

Classified according to quantity used for preservation of the foods. 

Class I -  More than 0.5 %       

Ø              Common salt

Ø              Sugar

Ø              Dextrose

Ø              Glucose syrup

Ø              Wood smoke

Ø              Spices

Ø              Vinegar or acetic acid

Ø              Honey

Class II :   Less than 0.5%

§               Benzoic acid including its salts

§               Sulphurous acid including its salts

§               Nitrates or nitrities of sodium or potassium

§               Sorbic acid including its sodium, potassium andlactic acid and calcium, phosphate

§               Nisin

§               Sodium and calcium propionate

The ideal antimicrobial preservative is :

Ø               Have a wide range of antimicrobial activity.

Ø               Nontoxic to human beings or animals.

Ø               Economical.

Ø               No effect on the flavour, taste, or aroma of the original food.

Ø               Not encourage the development of resistant strains

Ø               Kill rather than inhibit microorganism.

Mechanism of microbial inhibitors :

Ø              By interfering with the genetic mechanism of cell division or interference with cell membrane permeability.

Ø               Interference with the enzyme systems of the microbe by competing with the substrate for place on the active enzyme surface.

Ø               By inhibition of  biosynthesis of vitamins

Ø               By the formation of complexes with heavy metal ions.

Benzoic Acid

Ø              Also called phenylformic acid or benzenecarboxylic acid

Ø              Occur as colourless or white needless and its salt highly soluble in water

Ø              Occurs in cranberries, prunes, plumes, cinnamon, ripe clove and also in apples, strawberries 

Mechanism :

Undissociated molecules responsible for antimicrobial activity as it taken up by cells.

Interfering with the permeability of the microbial cell membrane.

General Effectiveness :

Most active against yeasts, bacteria, less active against    molds

Effective pH : 2.5 to 4.5

Metabolism : Conjugated with glycine to produce hippuric acid which is excreted

Application : Carbonated, non carbonated beverages, purees, concentrate, Jams, Jellies, preserves, Pie filling, Salad dressings, Pickles, Olives, Relishes.

Parabens

Ø              First described by Sabalitschka in 1924

Ø              Alkyl esters of  p-Hydroxybenzoic acid

Ø              Stable in air and resistant to cold and heat

Ø              Solubility increases from methyl to heptyl in ethanol

Ø              More active against mold and yeasts than bacteria

Ø              Effective pH-  Below 7.0 the parabens are weakly effective

Application -

Carbonated beverages and other soft drinks - a ratio of 2 methy to 1 propyl used

Beer -   12 ppm of n heptyl ester of p hydroxybezoic acid

Baked Goods – Used in fruit product, flavour extracts, pickles, olives, artificially sweetened James, jellies and preserve.

Acetic Acid and Acetates

General Effectiveness : Most effective against yeasts and bacteria and less extent against molds. Diacetate effective against rope and mold in bread.

Effective pH : From 3.5 to 5.5

Application :

Meals : Pickled sausages and  pigs feet. Vinegar packed sausages required minimum 3.6% acetic acid.

Bakery Products :  High concentration required. However, Sodium diacetate used in small concentration in bread and rolls. Traditional concentration 0.4 part to 100 part of flour.

Acid tasting Products : Used in catsup, mayonnaise, pickles, salad dressing.

Propionic Acid and Propionates

History : Antimicrobial properties were noted in 1913.

Physical Property : It is corrosive acid with strong odour.

Effectiveness : More effective against moulds but not effective against yeasts and bacteria.

Effective pH : 5.0 or 6.0

Mechanism : Accumulates in cells

                     Inhibities the enzyme of metabolism    

                     Competing with Alanine and other amino acids

Application :

Cheese : 8% Propionic Acid solution used in cheddar cheese

Butter : Propionate treated parchment wrappers provide protection

Bakery Products : Increase mold free life of bread by 8 days. Prevent rope formation in bread s even at pH level 6.0. Sodium salt used in cake and unleavened goods, and calcium salt in bread.

                                                                    

                         Sulfur Dioxide and Sulfites 

Historical records indicates that burning of sulfur was used by ancient, Egyptians and Romans in connection with their wine making

Physical Property : A colourless, non flammable gas has a suffocating odour and effect. 

Effective pH :  As the pH decrease, the proportion of H₂SO₃ increase and the bisulfite (HSO₃^- ) ion concentration decrease .

Action : A broad spectrum antimicrobial agents, inhibiting yeasts, moulds, and bacteria

Mechanism of microbial inhibition by Sulphur Dioxide :

1.    Inhibiting carbohydrate metabolism

2.    Reduction of bisulphate bond (S-S) in enzyme proteins.

3.    Inhibition of respiratory mechanism by halting the reaction involving nicotinamide dianucleotide.

Application - In dehydrated fruits, and vegetables, fruit juices, syrups, concentrates, purees and in wine making industry.

Fruit juices, syrups, Concentrates, Purees- 350-600 ppm

Wines-  During fermentation 50-100 ppm required

             During bulk storage 50-75 ppm required.

Fruit and vegetables for dehydration

Fruits exposed to SO₂ at 43_­^oC to 49^o C

Vegetable dipped in solution of neutral Sulfites and Bisulfites

Apricot, peaches – 2000 ppm

Pears-                    1000 ppm

Raisins                   1500 ppm

Apples  -                 800 ppm

Carrot and potatoes    200 to 250 ppm

Meat and fishes-     Help in eliminating black spot formation in shrimp.

Nitrates

Ø              Nitrite salt soluble in water but not in ethanol

Ø              Add directly or lipuid ingredient or produced by the action of nitrate reducing bacteria on a source of nitrate in the food

Ø              Effective pH- 5.0-5.5

Ø              150-200 ppm of nitrate inhibit clostridia in canned comminuted and cured meat.

                                                Hexamine

Ø           Acts as a preservative by slow breakdown to formaldehyde.

Ø           Used in canned fish and many other popular semi preserved specialties in Scandinavian countries and in the continent.

Dehydroacetic Acid

Ø           Insoluble in water, but soluble in the sodium salt.

Ø           Effective at all pH values and application is many perishable foods.

Ø           Effective at low pH concentration.

Ø           Used to control ripening in U.S.A.   

Carbon Dioxide

Gas at ambient temperature and solidifies at –78.5 C^o.

Effective - Effective against mould, and gram negative psychotropic bacteria

Mechanism : By exclusion of oxygen

                     Acidification of the cell interior

                     Interference with cellular enzyme

Used :          Evolved by meat products in gas permeable films.

          In MAP for beef, pork, poultry , and other food product.

Hydrogen Peroxide

History : H2O2 used as first antimicrobials preservative by French chemist L. J. Thenard in 1818 

Mechanism : >  Antimicrobial effect is due to its oxidative properties.
                       >  Bactericidal and sporicidal 

Application : Increase keeping quality of milk, cheese milk, cultured buttermilk, sour cream, egg and fish products. 

Fatty Acid Ester 

Ø              Certain fatty acid esters have antimicrobial activity in food.

Ø              Most effective is Glyceryl Monolaurate (monolaurin).

Ø              Effective against gram positive bacteria, molds, and yeasts.

Ø              Less effective against Gram negative.

Ø              Efficiency increase in presence of EDTA and inhibit Gram negative bacteria.

Glucose Oxidase 

§               Produce hydrogen peroxide by catalyzing the oxidation of glucose to Gluconic Acid.

§               Present in honey responsible for production for H­₂O­₂ as an inhibitory agents.

§               Inhibit bacteria include acinetobacter, Bacillus cereus, Salmonella etc.

Lactoperoxidase System

Ø              Molecular weight – 7,83,000 Daltion.

Ø              Glycoprotein with one heme group and 9.9-10.2% carbohydrates.

Ø              Present in raw milk, colostrums, saliva and other biological secretion.

Ø              Form antimicrobial compound reacting with Pseudohalogen Thiocyanate and Hydrogen Peroxide.

Ø              Disrupts cell function.

Ø              Damage the sugar and amino acid transport system.

Ø              Inhibits viruses, gram positive and gram negative bacteria, fungi.

Limitation :

Ø              Adhere to surfaces such as glass.

Ø              Inactivated by reducing compound and enzyme such as Horseradish Peroxidase.

Ø              Enzymes competing for H₂O₂ can reduce the inhibitory activity of LPS.

Ø              Inhibited by Suofhydryl containing compound (Cysteine) and by skim milk that received serve heat treatment.

Ovotransferrin

Ø              Albumen constituent of egg white

Ø              Have two iron binding sites each bound by anion

Ø              Effective ph - 9.5

Ø              Mechanism : functions by sequestering available ferric ion

Avidin

Chemical Nature  : Water soluble Glycoprotein

Source :          Egg albumin

Structure :      Made up of four identical Polypetides subunits

Mechanism :  >  Bacteriostatic agent

                       >  Binds biotin

Application :  Pharmaceuticals

Conalbumin

Source : About 10-12% of the total egg white solids.

Mechanism :  

• Binding of iron 
• Retard the growth of microorganism 
• Extend the lag phase of growth 
• Decrease the rate of multiplication

     Property : Sensitive to heat and 80% of the activity is lost with heating to 70-79^o C for 3 min.

Effectiveness : Gram positive are more effective than gram negative bacteria.

Indirect Antimicrobial

Compounds that are added to foods for purposes other than their antimicrobial effects.

Vanillic Acid :  Vanillic Acid and its ester used in fruits, bread and cheese spreads.

Boric Acid

Ø              Antimold

Ø              Used in treating citrus products which are to be shipped as fresh.

Ø              Application involve treating with 8% solution before Waxing. 

Borax (Sodium Tetraborate) :

Used to wash vegetables, whole fruits such as oranges.

Phosphoric Acid :

Used in some soft drinks e.g. Cola. 

Sugar

Mechanism : Make water unavailable to organisms  and to their osmotic effect.

Application : 

• Sweetened condensed milk, fruit in syrups. 
• Requires about six times more Sucrose than NaCl. 
• Pies, Cakes is stable due to high concentrations of sugar.

Sodium Chloride

Mechanism : 

• Reduce water activity and create unfavorable condition for microbial growth. 
• Causes high osmotic pressure and hence plasmolysis of cells. 
• Dehydrate foods by drawing out moisture. 
• Ionizes to yield the chlorine ion. 
• Reduce the solubility of oxygen in the moisture. 
• Sanitizes the cell against carbon dioxide. 
• Interferes with the action of proteolytic enzymes. 
• Relatively low concentration stimulates microbial growth whereas high concentration inhibits growth. 
• Inhibit pathogenic bacteria, toxic producing fungi.                  

Flavouring Agents

>  More antifungal than antibacterial.

>  Non lactic, gram positive bacteria are most sensitive.

>  Diacetyl is most effective flavouring agents.

Propylene Glycol

Ø              Also called 1,2 propanediol.

Ø              Prepared by propylene with chlorinated water to form the Chlorohydrin

Mechanism :    

• Reduce water activity. 
• Alters the permeability of the cell membrane.

Spices

Ø              Whole spices are more effective than spice extracts.

Ø              The antimicrobial activity of spices is due to presence of essential oils.

Ø              Gram positive organism more sensitive than gram negative organism.

Ø           Cinnamon, clove, and mustard are strong inhibitors while black pepper, red pepper and ginger are weak inhibitors.

Ø              Onions contains two Phenolic Compound : Protocatechuric Acid and Catechol.

Ø              Inhibition of microbial spoilage in mayonnaise based delicatessen salads with onion extract was demonstrated.

Ethanol

Ø               A colourless liquid, miscible in water and have boiling point of 78^o C.

Ø               Bactericidal but not sporicidial.

Ø               Denature protein in the cytoplasm at high concentration.

Ø               Reduce water activity at low concentration.

Ø               Used in sweet wines.

Ø               Approved for use as a direct antimicrobial in pizza crust not exceed 2% by product weight. 

Chitosan

Ø              A polycationic polymer obtained by alkaline hydrolysis of chitin from the shells of Crustaceae.

Ø              Destabilize the cell wall and cell membrane functions.

Ø              Effective against bacteria, yeasts and molds.

Ethyl Formate

Ø              A flammable liquid (C₃H₆O₂, -74)

Ø              Soluble in water about 10 parts.

Ø              Decompose into alcohol and free formic acid.

Ø              A yeast and mould inhibitor in nuts, dried fruits and cereals.

Ø              Permissible levels is 15 to 200 ppm. 

Methyl Formide

Ø              Also known as Bromomethane.

Ø              Colourless gas (CH₃Br, m.w. 94.95).

Ø              Free soluble in ethanol.

Ø              Fumigant and fungistat for dates.

Ø              Permissible level is 100 ppm.

Chlorine Dioxide

Ø                 Has the odour of chlorine.

Ø                 Unstable in light.

Ø                 Solubility in water is 3 g/l.

Ø                 Hydrolysis to Chlorous and Chloric Acid.

Ø                 Less than 1 ppm apply to decontaminate meat carcasses.

Ø                 Sodium and Potassium Nitrite used in curing of meat alongwith Sodium Erythorbate or Sodium Ascorbate.

Ethylene Diaminetetracetate                        

§                  Have no much antimicrobial effect.

§                  Destabilize the barrier functions of the outer membrane of the Gram negative bacteria and also of Gram positive bacteria.

§                  Enhance the antibacterial action of membrane acting chemicals like antioxidants, bacteriocins.

§                  Inhibit germination of C. Botulinin’s spore.

§                  Limitation : Divalent cations reduce the effectiveness of EDTA.

Bipehenyl

Ø           Used to control the decay of citrus fruit by Penicillia for long distance shipment

Ø           Generally impregnated into fruit wraps or sheets between fruit layer.

Benomyl

Ø      Applied uniformly over the entire surface of fruits

Ø      Applied at concentration of 0.5 to 1.0 g/l .

Medium Chain Fatty Acid

Ø              Medium chain fatty acids containing 12-18 carbons atoms are most effective.

Ø              Primarily bacteriostatic rather than bacteriocidal.

Ø              Lauric, Myristic and Palmitic effective against bacteria.

Ø              Capric and Lauric Acid effective against yeasts.

Ø              Inhibitory activity increase with the increase in double bonds in unsaturated fatty acids.

Ø              Undissociated form responsible for antimicrobial activity.

Antibiotics

Antibiotics are secondary metabolite produced by microorganism than inhibit or kill a wide spectrum of other microorganism.

Wood Smoking

Ø              Smoke generated by burning hardwood such as oak, walnut etc.

Ø              May be bacteriostatic or bactericidial and slight antifungal.

Ø              Contain volatile compound like Formaldehyde, phenols, cresols. May contain Aldehyde, waxes, Ketones, Acetaldehyde, resins, Guaiacol, and its methyl and propyl isomers, Catechol, Methyl Catechol, and Pyrogallol and its methyl ester.

Ø              More effective against vegetative cells than bacterial spores.

Ø              Used mainly for meat.

Ø              Liquid smoke similar in chemicals but has little preservative effect.

Limitation : 

• Contain carcinogenic chemicals like Benzopyrene and Dibenzanthracene so take little consumption of foods treated with smoke to reduce colon cancer.
•  It improve colour and have a tenderizing action on meats. 

Limitations

Ø              Toxicological data for natural antimicrobial are lacking and are as expensive to assemble as data for chemical compounds.

Ø              With the exception of Nisin, Natamycin and Lysozyme, no isolated naturally occurring antimicrobial are approved for use in foods by regulatory agencies.

Ø              Some of the chemicals used as preservatives are controversial in terms of the health risk involved and the benefits of extending the shelf life of the food.

Ø              The antimicrobial activity range of most known bacteriocins is narrow and does not extend to the Gram negative bacteria.

Ø              The amount of bacteriocin produced when a producing LAB is added to a food, is quite low due to insufficient growth of the LAB and absorption of the bacteriocin onto the food matrix.

Ø              The genetic information allowing for bacteriocin production in some cases is not stable.

Trends in Future

Ø              Vogler et al suggested a future preservatives that these consists of combinations of amino acids and fatty acids and are claimed to breakdown to their components which are readily digested in the usual way without any toxicity to the consumer.

Ø              Attempts are being made to replace the controversial chemicals with new antimicrobials or combinations of safe chemicals.

Ø              A proper study on the use of spices as antimicrobials agents will be helpful in avoiding or reducing the risk associated with the addition of chemical preservatives to foods.

Ø              Current research trends in food microbiology and food technology focus on mild, physical preservative techniques and the use of natural antimicrobial compounds.

Conclusions

 The naturally present antimicrobials and organic acids exhibit good inhibitory properties.