[Advances in Food Research] Advances in Food Research Volume 16 Volume 16 || Food Quality as Determined by Metabolic by-Products of Microorganisms

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  • FOOD QUALITY AS DETERMINED

    OF MICROORGANISMS BY METABOLIC BY-PRODUCTS

    BY M. L. FIELDS AND BONNIE S. RICHMOND Department of Food Science and Nutrition University of Missouri, Columbia Missouri

    AND

    RUTH E. BALDWIN

    Department of Food Science and Nutrition, and School of Home Economics University of Missouri, Columbia, Missouri

    I. Introduction ........................ ............................... II. Definition and Criteria for Chemical Indicators ...........................

    III. Chemical Indicators of Quality for Foods with High Protein Content .... A. Background .............................................................. B. Dominant Spoilage Flora ............................................... C. Chemical Indicators of Microbial Spoilage .............................

    IV. Chemical Indicators of Quality for Foods with High Fat Content ........ A. Background ........................... ........................ B. Dominant Spoilage Flora ............................................... C. Chemical Indicators of Microbial Spoilage .............................

    Content ...................................................................... A. Background ................................................. B. Dominant Spoilage Flora ..................................

    V. Chemical Indicators of Quality for Foods with High Carbohydrate

    C. Chemical Indicators of Microbial Spoilage ............................. VI. Research Needs .................................... .....................

    References ...................................................................

    161 162 163 163 167 168 198 198 198 199

    203 203 204 206 218 2 19

    1. INTRODUCTION

    Food quality is largely the sum of the characteristics which register favorably or adversely on an individual's senses. These characteristics include freshness, flavor, odor, texture, tenderness, consistency, color, size and shape, degree of ripeness, and presence or absence of defects. Nutritive value, chemical residues, and disease-producing organisms are also a part of food quality, although these are not measured by the senses of smell, taste, sight, or touch.

    ' Formerly with Dept. of Horticulture, University of Missouri. 161

  • 162 FIELDS, RICHMOND AND BALDWIN

    When one visualizes a spectrum ranging from good to poor quality, the extremes are easily differentiated. This is not true for the central part of the spectrum, however, especially for products in which the manufacturing process tends t o mask differences, as with comminuted foods. When foods become more abundant, standards of quality are likely to be higher and more clearly defined. Quality which is acceptable in one society may not be in another.

    The consumer and many manufacturers depend upon the senses of smell, taste, sight, and touch for evaluating food quality. These organoleptic methods are qualitative and vary from individual to individual. The need for more adequate evaluation has focused atten- tion on chemical compounds which can be used for differentiation. Certain compounds arising from the metabolism of the dominant spoilage organisms answer this need and can be classified as chemical indicators of food quality.

    Chemical indicators may be the only means of evaluating quality in some foods, since processing methods, such as filtration, preclude the use of conventional methods such as plate counts. In some foods, indicator compounds may supplement microbiological methods of analyzing food quality, including plate counts, mold counts, rot fragment counts, and direct microscopic counts. The use of chemical indicators will assist the manufacturer in producing and maintaining high-quality foods.

    II. DEFINITION AND CRITERIA FOR CHEMICAL INDICATORS

    A chemical compound which indicates deterioration due to micro- organisms may be defined as a metabolic by-product which is produced by the dominant spoilage organisms as a result of their growth in the food. The dominant spoilage flora is that group of microorganisms which persists and brings about deterioration in the quality of a food under the usual handling and storage conditions. Since a specific spoilage situation may involve a mixed culture, measurement of multiple compounds may be superior to the use of a single metabolic by-product as an indicator of quality.

    Fields (1964b) proposed the following criteria for a chemical indicator of quality of foods: (1) The compound must be present a t low levels or absent in sound foods. (2) With increased spoilage, there must be an increase in the amount of the indicator. (3) The compound should make it possible to differentiate low-quality raw materials from

  • QUALITY EFFECTS OF MICROORGANISM BY-PRODUCTS 163

    poor processing conditions. (4) The indicator should be produced by the dominant spoilage flora. Farber (1952) stated that a spoilage index must be as reliable as organoleptic criteria and should indicate stages of spoilage which cannot be established definitely by organoleptic testing. To be useful as an index of quality for seafood and ground beef, the test for the compound must be rapid and the analysis must be simple (Novak et al., 1956; Rogers and McCleskey, 1961). Patterson (1945) emphasized that the compound should never yield a false positive test, and for this reason a companion test is desirable. It is true that some metabolic by-products of the dominant spoilage flora also might arise by autolysis, but the amount of the compound would be markedly lower than the levels associated with spoilage due to microorganisms.

    Table I summarizes the characteristics of potential and suggested chemical indicators of food quality. The suitability of the potential indicator may be determined, in part, by its physical properties. Compounds with low boiling points would be unsatisfactry where the use of heat in manufacturing or processing would volatilize them. Solubility of the compounds would affect the method of analyses. For example, acetic and formic acids can be removed from foods by steam distillation, while lactic acid must be extracted with ether or other solvents.

    Some of the chemical indexes may be very acceptable in certain foods but not in others. Acetylmethylcarbinol is a valuable constitutent of the flavor components in butter. In apple juice, however, the presence of large quantities indicates the use of unfit raw materials and/or poor sanitary conditions in the processing plant (Fields, 1962a). If the chemical compound has a useful function as a component in the food, it cannot be used as a chemical indicator of the quality of the food. One may compare the presence of a chemical indicator to the presence of some microorganisms in foods. Penicillia are very essential in producing certain cheeses but are detrimental to quality when they grow in citrus fruits and produce decay.

    111. CHEMICAL INDICATORS OF QUALITY FOR FOODS WITH HIGH PROTEIN CONTENT

    A. BACKGROUND

    Research on the quality of high-protein foods as indicated by meta- bolic by-products of microorganisms .has centered on seafoods, pro- bably because they are so highly perishable. Studies on the decomposi- tion of fish have been conducted by processors and by governmental

  • TABLE I SUh4MARY OF CHARACTERISTICS OF CHEMICAL hDICATORS OF MICROBIOLOGICAL QUALITY

    Solubility ( s ) Boiling point Cold Alcohol

    Indicator Description ("C) water acid, etc.

    Acetic acid

    Acetylmethylcarbinol Liquid above 15OC with a pleasant

    Clear, colorless acid, liquid C,H,O, Pungent odor

    (AMC, acetoin, 3-

    butanone) Ammonia

    N H 3 Butyric acid

    Diacetyl (biacetyl,

    odor, a product of fermentation hydroxy-2-

    Colorless gas, pungent odor. Lower

    Colorless, limpid liquid. Rancid odor

    Yellowish green liquid. Quinone odor

    limit for human perception, 53 ppm

    C,H,O,

    C*H,O, 2, 3-butanedione)

    Dimethylamine Gas, strong arnmoniacal odor C,H,N

    Ethyl alcohol (ethanol) C,H,OH

    Formic acid Colorless, fuming liquid. Pungent CHZOZ penetrating odor. Dangerously

    Clear, colorless, flammable liquid

    caustic

    needles Galacturonic acid White powder, forms monohydrate

    118.1

    148.0

    - 33.35

    163.5

    88.0

    7.4

    78.5

    100.7

    S

    S

    very s

    S

    S

    S

    S

    S

    S

    s alcohol

    S

    s alcohol; ether

    s alcohol; ether

    S

    s alcohol; ether

    s alcohol; ether

    slightly s hot alcohol; insoluble ether

  • Histamine C,H&

    Hydrogen sulfide H,S

    Indole

    Lactic acid C*H,N

    C3H603

    Oleic acid

    Palmitic acid

    Propionic acid

    Stearic acid

    Succinic acid

    Trimethylamine

    Tryptophane

    c I sH34Oz C,tlH,,OZ

    C3H60,

    ISH36'Z

    C4H604

    C 3 H P

    C,IH,,N*O

    Valeric acid C5HlOO2

    Yellow crystals (needles) from water, has medical uses, occurs as a result of putrefaction

    Colorless gas, flanlmable, offensive odor, sweetish taste, dangerously poisonous

    intense fecal odor Colorless to yellowish scales,

    Colorless to yellowish syrupy liquid

    Colorless or nearly so, odorless

    White, crystalline scales liquid

    Clear, colorless liquid. Pungent odor

    White leaflets

    Colorless crystals. Odorless. Acid

    Gas, pungent, fishy ammoniacal

    Essential amino acid for rats. Found

    taste.

    odor

    in casein and other proteins Used as nutrient for humans White crystals

    Disagreeable odor and taste Clear, colorless liquid

    209-210

    -60.8

    253-254

    122.0

    286.0

    215.0

    141.1

    383.0

    235.0

    3.2-3.8

    187.0

    S

    S

    S

    ins

    ins

    S

    slightly s alcohol

    s alcohol

    very s alcohol; ether s benzene

    s alcohol; ether glycerin; insoluble chlorine, petroleum ether

    S

    slightly s in cold; very s in hot

    s alcohol; ether

    slightly s s

    S sp. s alcohol; ether

    very s

    slightly s s hot alcohol

    very s alcohol; slightly ether, benzene

    insoluble chlorine

    slightly s alcohol; ether

  • 166 FIELDS, RICHMOND AND BALDWIN

    TABLE II BACTERIA AND FLOIENTOUS FUNGI CAUSING SPOILAGE OF EGGS AND SEAFOOD

    Product Spoilage organism Reference

    Eggs Pseudomonas fluorescens Pseudomonas sp., Achromabacter sp.

    Proteus sp.

    Mucor, Thamnidium, Botrytis, Alternaria, Cladosporium, Penicilliwn, Sporotrichwn

    Alcaligenes. Flauobacterium, Paracolobactrum

    Fish, salt Serratia, Micrococcus, Bacillus, Achromobacter, Pseudomoms

    Flavobacterium, Achromobacter, Escherichia, Bacillus, Serratia

    Achromobacter , Micrococcus , Kurthia , Pseudomonns, Flavobacterium, Proteus

    Staphylococcus, Pseudomonns,

    Frazier, 1958 Frazier, 1958; Florian and

    Frazier, 1958; Florian and

    Frazier, 1958.

    Trussell, 1957.

    Trussell, 1957.

    Florian and Trussell, 1957.

    Frazier, 1958.

    Griffiths, 1937.

    Snow and Beard, 1939.

    Shellfish Flauobacterium, Pseudomonas, Bacillus, Frazier, 1958. Proteus, Achromobacter.

    agencies charged by law with regulation of the purity of our food supply.

    Because of the extreme perishability of some products, decomposed foods get into market channels occasionally. For example, the U. S. Department of Health, Education, and Welfare (HEW) (1966) publish- ed Notices of Judgment under the Federal Food, Drug, and Cosmetic Act which include seizures due to decomposed material in frozen eggs (FNJ 30337, 30338, 30340, 30341, 30342, 30343, 30345), frozen red snapper (FNJ 30351), frozen flounder fillets (FNJ 30354), and fro- zen salmon (FNJ 30356).

    The chemical composition of the food and the metabolic activities of the organisms growing in the food determine the compounds which can be used as indicators. Although the high-protein foods (8.4- 25.2y0) included in this discussion contain 0.8-14.5% fat and 0.0-1.770 carbohydrate, our concern here is with compounds derived from the protein. It must not be overlooked, however, that substances arising from components other than protein may have a potential as indexes of decomposition. Used to detect spoilage in the past have been ammonia nitrogen, reducing substances such as dextrose, acidity of the fat, and bacteriological examination (Macomber, 1927).

  • 167 B. DOMINANT SPOILAGE FLORA

    The dominant spoilage floras for eggs and sea foods are listed in Table II. Molds cause spoilage in eggs, but to a lesser extent than do bacteria. Many of the bacteria which cause decomposition in fish may also be responsible for loss of quality in eggs. The dominant flora of fish is composed of species which grow in the sea. The organisms are mainly gram-negative rods present in the slime covering the surface of the fish. Since these bacteria are psychrophilic, spoilage may pro- ceed even under conditions of refrigeration or icing.

    According to Zobell (1946), marine bacteria are actively proteolytic, and they rapidly attack most kinds of proteinaceous materials. Nearly all of them liberate ammonia from peptones, but only a few produce indole from tryptophane. Zobell also stated that marine bacteria are weakly saccharolytic.

    QUALITY EFFECTS OF MICROORGANISM BY-PRODUCTS

    TABLE III

    NINE GENERA"^ PRODUCTION OF SELECTED METABOLIC B Y PRODUCTS BY 143 SPECIES OF

    Number of species

    Indicator Positive Negative

    Ammonia 60 0 Indole 2 58 Hydrogen sulfide 31 29 Hydrolyzed fat 13 47

    Achromobaeter. Flouobaeterium, Pseudomonos. Serratia, Microeoecw, Actinomyces, Vibrio, Bacterium,

    *Compiled from Zobell and Upham. 1944. and Bacillus.

    TABLE IV PRODUCTION OF SELECTED METABOLIC BY PRODUCTS BY 143 SPECIES OF

    EIGHT GENERA'.^ Number of species

    Indicator Information

    Positive Negative not given

    Ammonia Indole Trimethylamine Hydrogen sulfide

    29 14 6

    14

    7 107 101 28

    8 129 34 95

    aA chmmobacter . Flouobacterium , R e d o m o n a s , Sorcina , Serratia , A lcaligenes , Proteus, Kurthia , and bCompiled from Bergeys Manual of Determinative Bacteriology (Breed et al., 1957).

    Microeoccus.

  • 168 FIELDS, RICHMOND AND BALDWIN

    If the breakdown is aerobic, the process is called decay, whereas a breakdown that is anaerobic is called putrefaction. When putrefaction occurs, various foul-smelling compounds are produced. These arise as a result of bacterial action on amino acids and include mercaptans, indole, hydrogen sulfide, ammonia, amines, and organic acids. If the protein is well aerated, digestion occurs and no ill-smelling compounds are formed.

    The enzyme systems of microorganisms causing spoilage of protein include proteinases, peptidases, deaminases, and decarboxylases. The amino acids freed by the action of peptidases and the breakdown pro- ducts of amino acids resulting from deaminase or decarboxylase activity have been suggested as chemical indicators for the quality of protein foods. Other suggested compounds include succinic, formic and acetic acids, ammonia, indole, and hydrogen sulfide. Tables 111 and IV list genera of microorganisms and the number of species of these genera which are known to produce ammonia, indole, trimethylamine, or hydrogen sulfide.

    C. CHEMICAL INDICATORS OF MICROBLAL SPOILAGE

    I. Ammonia

    a. Biosynthesis of Ammonia. Ammonia is a metabolic by-product of several bacteria which hydrolyze proteins. In fish, one of the principal sources of ammonia is urea (Elliott, 1952). As described by Salle (1961), ammonia is produced in conjunction with other products of enzyme action:

    1. Production of a fatty acid and ammonia by deamination, de- car...

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