484

Journal ofFood Protection. Vol. 45, No.5, Pages 484-491 (Aprill982) Copyright International Association of Milk, Food, and Environmental Sanitarians

Recent Developments in Intermediate Moisture Foods

L. E. ERICKSON

Department ofChemical Engineering, Kansas State University, Manhattan, Kansas 66506

(Received for publication March 9, 1981) Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021

ABSTRACT HISTORY OF INTERMEDIATE MOISTURE FOODS

The science and technology of intermediate moisture foods Modification of foods to increase shelf-life has been has advanced during the last 25 years. Developments during going on for many years. Food preservation based on the this period are reviewed. Knowledge of the relationship of water lowering of water activity to a level at which microbial activity and food degradation has advanced considerably growth is prevented or reduced has been going on since during this period. Many new intermediate moisture foods have sun-dried foods and salted foods were first developed. been developed. Several methods have been developed to alter Referen~es to sun drying can be found in the Bible, the water activity offoods. ancient Egyptian hieroglyphics and in the journals of Marco Polo (17). Salting and sugaring of foods also have a long history. However, an understanding of the Intermediate moisture foods are foods with moisture importance of water activity in food preservation was content between dry foods which can be stored at room advanced significantly in 1957 with the work of Scott temperatures and moist foods which need to be frozen, (28). lt is clear that water activity and modification of refrigerated, canned or preserved by some other water activity have become central considerations in the mechanism. A precise definition of intermediate development of intermediate moisture foods (4,6, 7,8,13, moisture foods based on water content or water activity 15,17,20,24,28,30). has not evolved. According to Karel (15) traditional Examples of traditional intermediate moisture foods intermediate moisture feeds have moisture contents include dried fruits such as prunes; products to which between 10 and 40o/o and water activities from 0.65 to sugar has been added, such as candies, marshmallows, 0.90. Corry (7) has pointed out that the water activity jams and pie fillings; dried products with salt and sugar, range of intermediate moisture foods differs from author added such as hams, and bakery products, such as fruit to author with values ranging from 0.70- 0.85 (4), 0.60 - cakes. Table 1 shows the water activity of some 0.85 (24), 0.70 - 0.90 (13), and 0.60 - 0.90 (6). Corry (7) traditional intermediate moisture foods (15). points out that a range of water activities from 0.70- 0.90 for intermediate moisture foods is reasonable because TABLE L Water activity of selected traditional intermediate moisture foods (15). foods with water activities below 0.7 are stable for considerable lengths of time with respect to microbial Food Water activity spoilage and can be classified as "dry", and foods with a Liverwurst 0.96 water activity of0.90 or below do not support growth and Salami 0.82-0.85 toxin production by most bacteria. 'Landjiiger' sausage 0.79 Kaplow (12) defines intermediate moisture foods as, Dried fruits 0.72-0.80 "An Intermediate Moisture Food is one which can be Jams and jellies 0.82-0.94 eaten as is, without rehydration, and yet is shelf-stable Honey 0.75 of commercial 0.65-0.71 without refrigeration or thermal processing" (8). In the development of intermediate moisture foods, Robson (26) has pointed out that reduced spoilage, improved safety. There are three important recent developments with increased shelf-life and retention of soft moist texture are respect to intermediate moisture food products. Develop­ important considerations. Reduction of water activity is ment of intermediate moisture pet foods has been most frequently necessary to develop an intermediate moisture successful (5,8). A large fraction of the current market is food which is shelf-stable without refrigeration. ftlled with these products. The development of extrusion

JOURNAL OF FOOD PROTECTION. VOL. 45, APRIL 1982 INTERMEDIATE MOISTURE FOODS 485

cooking to produce most of these pet food products is TABLE 4. Characteristics of some recently developed inter- also significant (10). The second development in food mediate (15). products includes intermediate moisture foods for Characteristic IMFCatfish IMF Coconut milk IMF Cheese defense, space flights, explorers and others on extended 0.8 0.75-0.8 0.82 missions (11 ,15,26). The third is development of new ~ Water (o/o) 26.6 30-35 "-'25 intermediate moisture foods for the general public (8). pH 6.4 7 5.2 Table 2 shows the formula for a soft moist pet food Additives K-sorbate 0.1 o/osorbic acid K-sorbate (11). Table 3 shows the formula for one of several new P.G.a P.G. intermediate moisture foods developed by Swift and Sorbitol NaCl Company for the U.S. Air Force (11). Tables 4 and 5 Sucrose show some of the important characteristics of some other NaC1 intermediate moisture products developed for the ap .G. Propylene glycol. defense and space programs (15). Table 6 shows some of the intermediate moisture foods which were found in the Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021 supermarket (8). TABLE 5. Analysis of example intermediate moisture foods (15). TABLE 2. A typical soft, moist (intermediate moisture) pet Water Average food formula (ll)a. Cubes content percent pH Water Ingredients Parts by weight (%) salt activity Chopped meat by-products (tripe, udders, Roast beef 22.2 3.0 5.75 0.79 cheek trimmings, tongue trimmings, Barbecue beef 16.2 2.7 5.05 0.66 gullets, etc.) 32.0 Roast pork 22.4 3.6 5.70 0.74 Defatted soy flakes 31.0 Barbecue chicken 19.7 4.0 5.20 0.70 Sucrose 21.7 Chicken a Ia King 14.9 3.6 5.90 0.61 Flaked soy bean hulls 3.0 Beef stew 17.3 3.7 5.80 0.65 Dicalcium phosphate 3.0 Corned beef 16.2 5.4 5.85 0.62 Dried non-fat milk solids 2.5 Chili with beans 13.9 2.6 5.65 0.79 Propylene glycol 2.0 Sausage 24.2 4.5 4.90 0.78 Bleachable-fancy tallow 1.0 Ham 19.9 4.5 5.90 0.72 Mono- and diglycerides 1.0 Sodium chloride 1.0 Potassium sorbate 0.3 TABLE 6. Intermediate moisture food products noted on FD&Creddye 0.006 supermarket tour (8). Garlic 0.2 Vitamin and mineral premix 0.06 Type Name Manufacturer aFrom U.S. Patent 3,202,519 (1965). Historical Jams, jellies Sausage Some cheese TABLE 3. Formula of ready-to-eat intermediate moisture "Dried" fruit ham cubesa (11). Marshmallows Many Ingredients "Toby weight Honey Country hams Ham, cooked, ground, freeze dried 45.00 Jerkey Water, distilled 10.000 Salted fish Water as steam 12.4215 Maple syrup Non-dairy coffee whitener 6.30 Glycerol 6.00 Traditional Pop-Tarts Kellogs Pregelatinized starch 5.50 Slim Jims General Mills Gelatin (175 bloom) 5.00 Hostess pies ITT Continental Sorbitol, dry 3.00 Ready to spread General Mills Sucrose 2.20 frosting Hydrolyzed vegetable protein, Ham 2.00 Cereal 1.50 Semi-Traditional Breakfast squares General Mills Monosodium glutamate 0.46 Pie sticks General Mills Liquid smoke (Char-Oil) 0.35 Pizza crust Fairmont Foods Sorbic acid 0.20 Ascorbic acid 0.045 Novel Pet foods Ribotide 0.02 Infusion cooked Citric acid 0.0035 Extrusion-particles Many Total 100.0000 Extrusion-patties a Developed by Swift & Company for U.S. Air Force. Food sticks Pillsbury

JOURNAL OF FOOD PROTECTION. VOL. 45, APRIL 1982 486 ERICKSON

TECHNOLOGY OF INTERMEDIATE MOISTURE FOODS Humectants may be added to develop intermediate moisture foods with more favorable water sorption The technology of intermediate moisture foods may be isotherms. Salt is an example of an excellent humectant. divided into several parts. The food science associated Addition of salt to the food reduces water activity with with characterization of these foods is one aspect. The only a small reduction of moisture content; that is, the stability of intermediate moisture foods under various curve in Fig. 1 is shifted to the left by adding humectants. storage conditions and the associated chemical and In characterizing intermediate moisture foods, it is microbial processes of degradation are another part. The important to realize that water activity and water technology of developing a new intermediate moisture sorption isotherms are part of the science of equilibrium food, including the processing and selection of thermodynamics. The adsorption and desorption iso­ ingredients, is another consideration. The nutritional therms frequently do not agree with each other and aspects ofthese foods is also important. hysteresis is observed. Moreover, repeated experiments Characterization may reveal a slowly shifting water sorption isotherm (9).

An important method used to describe a food product The shifting and hysteresis occur because equilibrium Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021 is a list of the ingredients, including the moisture content conditions are not attained. In spite of these problems, and amount of each ingredient. Since microbial water activity is a useful concept for characterizing degradation offood products is related to water activity, intermediate moisture foods. this is an important characteristic of intermediate Water activity is the ratio of the fugacity, f, at the moisture foods. The water sorption isotherm which conditions encountered to the fugacity at a chosen

relates water activity and moisture content is an standard state, f0 (25,31). Thus, the numerical value of important relationship. Figure 1 shows the water activity and the physical significance of numerical values sorption isotherm for intermediate moisture tortillas (23). depends on the choice of standard states. The standard The shape of the isotherm depends on temperature and state which is most widely used for water in foods is the ingredients in the food (20). The shape of the isotherm is fugacity of the pure solvent (water) at the temperature important because frequently the taste and texture are and pressure of the system. At the pressures normally related to moisture content. Achieving a soft, moist encountered in foods, the fugacity is essentially equal to intermediate moisture food frequently requires develop­ the vapor pressure and the standard state fugacity is the ing a food with as high a moisture content as possible for vapor pressure of pure water at the temperature of the an acceptable water activity. system. The fugacity of the water in the food may be taken as the equilibrium partial pressure at low pressures. Thus the activity, aw, becomes 40 f p aw P ERH -Ill f';; = 0 = :E where P is the partial pressure of the water vapor in 0 Ill equilibrium with a food product with a certain water Cl content and P 0 is the vapor pressure of pure water at the 0 Q 30 temperature of the food. Thus the activity is equal to the ...... equilibrium relative humidity, ERH, at the temperature 0 N of the food. The values of water activity given in this :::X: paper are all for the standard state defined above. Cl Stability 1- The stability of intermediate moisture foods is very z 20 w important. Much of the research with intermediate 1- z moisture foods is concerned with the rate and extent of 0 u degradation under various storage conditions and the w ... effect of additives and water activity on stability a:: (1,2.3.7,8,15,17,18,21,22,23,27,28,30,35). Food quality ::::> 1- 10 / may change under storage conditions because of (/) enzymatic reactions, non-enzymatic browning reactions, 0- lipid oxidation and reactions between lipids and ~ proteins. Microbial degradation of foods may be due to bacterial growth, yeast growth, mold growth and production of toxins and other undesirable microbial 00~--~--~--~----~---L--~ 0.2 0.4 0.6 0.8 1.0 products (14,21,35). Water activity is an important WATER ACTIVITY variable for most of these processes. Labuza (8,16) and Rockland and Nishi (27) have shown how water activity Figure 1. Water sorption isotherm at 25 C for intermediate affects these processes. Figure 2 shows the results of moisture tortillas (23). Labuza (8,16); however, the reader should realize that

JOURNAL OF FOOD PROTECTION. VOL. 45, APRIL 1982 INTERMEDIATE MOISTURE FOODS 487 these results depend on chemical composition. Labuza German workers. Rockland and Nishi (27) showed that (8,34) has shown that the addition of solutes influences enzyme activity increases with water activity. the browning rate (see Fig. 3). Figure 3 shows that Non-enzymatic browning in intermediate moisture humectants which are added to lower water activity may foods must be carefully examined because high rates of influence the browning rate. browning may occur at these water activities (14,16,17, 18,19,34,35). Figure 3 shows that sorbitol reduces the rate ofbrowning. Labuza (18) attributes this to the effect ,.....-----,, of sorbitol on viscosity. Williams (35) has pointed out / --0 ...... w / ... I ..I '" that the observed maxima in browning rates have been ~ I attributed to a balance of viscosity-controlled diffusion, a:: s::::.tj .,,.. I z (,)10 ~ ;r:C dilution and mass action effects. At low water activities 0 ;:: (,)"' ii tj ~ diffusion may limit reaction rates. Dilution of the 0 <( :i;o c:>f/1/ ~I w ~ o .. <>c}~-o reactant may reduce the rate at higher water activities. a:: ~-i? _,, .. ,~,

Higher water activities also retard reversible reactions Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021 w ~~ j .. E9.ll > /'"''·"''!' which produce water. Up to 3.5 moles of water are ti / / ;"' lt; .J / /o "' c ,;J;o formed per mole of sugar consumed in non-enzymatic w //' Staphylococcus aureus (21). A enzymatic reaction and the products must leave the site. water activity of less than 0.7 greatly improves the Karel (14) also points out that much research on stability of intermediate moisture foods; however, enzymatic reactions in food is being carried out by decreasing the water activity to this low level is frequently

JOURNAL OF FOOD PROTECTION, VOL. 451 APRIL 1982 488 ERICKSON not desirable because the quality of the product is better successfully as humectants in many traditional inter­ at higher water activities. mediate moisture foods. They are also important In the preparation of intermediate moisture foods, it is humectants in developing new intermediate moisture important to minimize initial microbial contamination. foods. Table 7 shows that the concentration and water Heat processing to destroy microorganisms and inacti­ activity of several aqueous solutions which may be used vate enzymes is often desirable. Hygienic or even aseptic to reduce the water activity of foods. Kaplow (12) has conditions should be used in preparing intermediate described two methods to achieve a desired water activity moisture foods. If possible, intermediate moisture foods in an intermediate moisture food. One of these methods should be vacuum-packaged in containers impermeable is to bring the food to equilibrium with a solution of the to oxygen (21). Chemical preservatives may also be used desired water activity. Other preservatives may also be in to control yeast and mold growth. Sulfurous acid, the solution. Tables 8 and 9, respectively, show the benzoic acid, parahydroxybenzoic acid, sorbic acid and equilibration solutions and the results of using such diethyl pyrocarbonate and related salts (,12) may be used solutions to prepare foods with reduced water content as to control yeast growth. well as reduced water activity (4). Table 9 also breifly Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021 describes the processing associated with each of the DEVEWPMENT OF INTERMEDIATE MOISTURE products. FOODS TABLE 8. Composition ofequilibration solutions for products Recently, a number of intermediate moisture foods in Table 9 have been developed (4,5,8,11,12,15,23,26,30). The Products science and technology associated with the synthesis of Components of Maca- Pine- new intermediate moisture foods may be divided into solution% Tuna Carrot roni Pork apple Celery Beef methods to achieve the desired water content and water Glycerol 53.6 59.2 42.7 45.6 55.0 68.4 87.9 activity and methods to maintain product stability. The Water 38.6 34.7 48.8 43.2 21.5 25.2 texture, taste and appeal ofthe product must be carefully Sodium chloride 7.1 5.5 8.0 10.5 5.9 10.1 considered in developing a new food. Sucrose 23.0 0.6 0.5 0.7 0.5 0.5 Water activity modification K-Sorbate 0.7 Na-Benzoate 2.0 Frequently, water is added or removed in producing a new intermediate moisture food. Of the many methods of The second method described by Kaplow (12) involves removing water, freeze-drying appears to be one of the contacting the food with a solution for a short time under best from the view point of maintaining product quality. conditions such that the desired final product water Kaplow (12) has reported that shrinkage and toughness activity and composition are achieved. This is a are frequently associated with other drying processes. nonequilibrium method. Table 10 shows the composition Removal of water reduces water activity, but the soft of an infusion solution for freeze dried carrots (12). moist texture desired in intermediate moisture foods is The adjustment of composition and water activity may lost if too much water is removed. involve either removal of water or addition of water. Addition of humectants to foods reduces water Because of hysteresis in the water activity vs. moisture activity. Propylene glycol, for example, reduces water content curve, two different measured water activities activity and acts as a plasticizing agent to help achieve a may be obtained for the same moisture content when desired texture (12). Salt and sugar have been used these two different methods are used. Usually the true equilibrium water activity will be between these values. As shown by Troller and Christian (33), the magnitude of TABLE 7. Water activity of aqueous solutions of some the hysteresis is larger at low temperature where rate potential food humectants (22 C) (23). processes are slower. Figure 4 shows that hysteresis is greatest at 5 C, visible at 45 C, but not visible at 60 C for Concentration Approximate water Humectant %wt/wt activity raw chicken. Plitman et al. (24) have shown that the growth of S. aureus, at the same measured water activity, Sucrose 58.4 0.90 is greater for samples prepared by desorption than by 67* 0.86 adsorption; that is, the samples with the greater moisture Glucose 47* 0.92 Invert sugar 63* 0.82 content showed more growth. This result is expected Sucrose 37.6%and 75* 0.71 because true equilibrium was not present at the start of Invert sugar 62.4% these experiments. Thus both the apparent initial water NaC1 9.3 0.94 activity of the prepared intermediate moisture food and 19.1 0.85 the equilibrium value for that moisture content should be 27* 0.74 considered in preparing new foods. Lactose 14.5* 0.99 Karel (15) and Heidelbaugh and Karel (11) have Maltose 48.8* 0.95 divided the process of water activity modification into (a) * Saturated solution. "moist-infusion" in which normal-moisture solid food

JOURNAL OFFOOD PROTECTION, VOL. 45, APRIL 1982 INTERMEDIATE MOISTURE FOODS 489

TABLE 9. Preparation ofrepresentative intermediate moisture foods by equilibration (4). Ratio: a Initial Wt. _~Equilibrated product Initial material Solution Wt. Processing Hz()o/o 3w Tuna, canned cold water pack 60.0 0.59 soak 38.8 0.81 pieces 1-cm thick

Carrots cook diced0.9cm 88.2 0.48 95-98 c 51.5 0.81 cooked refrig

Macaroni, elbow cook cook, drain 63.0 0.43 95-98C 46.1 0.83

refrig Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021

Pork loin, raw cook 1 em thick 70.0 0.73 95-98 c 42.5 0.81 refrig

Pineapple canned, chunks 73.0 0.46 soak 43.0 0.85

Celery cold 0.6 em cross cut 94.7 0.52 soak 39.6 0.83 blanch

Beef, ribeye cook 1-cm thick 70.8 2.35 95-98 c 0.86 a For composition of equilibration solutions see Table 8.

TABLE 10. Soak infusion of freeze-dried carrots with water activity ofO. 77 (12). Infusion Final Component solution product 25 -(/') Glycerol 54.4% 51.1 'Vo ~ Carrot Solids 6.3 (I) Water 42.0 39.3 >-cr Sodium chloride 2.2 2.1 0 Propylene glycol 1.1 0.9 0~ Potassium sorbate 0.3 0.3 100.0% 100.0% - 1-z UJ 1- pieces are soaked and/or cooked in an appropriate z 0 solution to obtain a product with the desired water (.) activity, (b) "dry-infusion" in which solid food pieces are cr first dehydrated following which they are infused by w soaking in a solution containing the desired osmotic ~ agents and (c) "blending" in which the components are 3: weighed, blended, cooked and extruded or otherwise combined to obtain a product with the desired water activity (11). "Moist-infusion" is similar to the equilibri­ um method of Kaplow (12). Tables 8 and 9 refer to products prepared by this method. "Dry-infusion" is closely related to the second method of Kaplow (12). Freeze dehydration of solid ingredients followed by blending in a low-speed mixer preceeded infusion for the Figure 4. Adsorption ( ) and desorption (----)for raw intermediate moisture foods prepared by this method chicken at three temperatures. Adsorption and desorption data (1 1). The products described in Tables 3 and 5 were were identical at 60 C (33).

JOURNAL OF FOOD PROTECTION, VOL. 45, APRIL 1982 490 ERICKSON prepared by this method. The "blending'' method is used In the development of intermediate moisture foods, in production of many intermediate moisture pet foods, additives are frequently used to reduce the rate of such as the one shown in Table 2. chemical deterioration of foods. The methods of control Product stability have been discussed above. The ingredients in a large number of intermediate moisture foods have been Development of intermediate moisture foods fre­ quently involves use of additives to improve product presented by Heidelbaugh and Karel (II). Flink (8) has stability, appropriate packaging and processing to listed the ingredients of a large number of intermediate inactivate enzymes and destroy microorganisms. Heidel­ moisture foods found in supermarkets. Citric acid has baugh and Karel (II) have pointed out that heating been added as an antioxidant in many of these foods. and/or chemical additives are frequently used for Sorbitol has been added to reduce nonenzymatic microbiological stabilization, that blanching is often browning and as a humectant. used to inactivate enzymes and that physical/chemical Packaging is important in protecting the quality of deterioration is prevented by addition of antioxidants, intermediate moisture foods. For many of these foods, the package needs to be impermeable to water vapor. chelators, emulsifiers or stabilizers. Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021 In the development of intermediate moisture tortillas, Impermeability with respect to oxygen can help prevent potassium sorbate was added as a mycostatic agent to oxidation. Karel (14) has identified several factors which help control yeast and mold growth (23). Heat treatment are important in packaging intermediate moisture foods. also helped to reduce the initial microbial population. He has shown that browning and increases in moisture A number of food additives which can be used as content with storage time can be predicted for different packaging materials. mycostatic agents have been investigated. Karel (15) has reviewed the literature and pointed out that most mold inhibitors are not effective by themselves against S. SUMMARY aureus at water activities of 0.86-0.90 and pH of 5.6. Acidification to pH 5.2 improves the effectiveness of There are a number of recent developments in these inhibitors. A combination of 4-6 o/o propylene glycol intermediate moisture foods. The effect of water activity with 0.1 to 0.3% potassium sorbate or calcium on microbial growth has been extensively investigated. A propionate is effective as a microbial inhibitor at pH 5-6 number of humectants are available to reduce water {15). Table 11 shows the relative effectiveness of several activity to acceptable levels. Several antimycotic agents inhibitors in preventing mold growth (15). have been investigated to control yeast and mold growth. The effect of water activity on enzymatic and oxidative degradation processes is understood reasonably well. TABLE 11. Time of mold appearance on H ennican (pH 5.6) Rates of nonenzymatic browning have been found to vary (15). with the concentration of various humectants. Sorbitol appears to decrease the rate of browning by increasing Inhibitor o/o Level (w /w) Day of appearance viscosity. Methyl paraben 0.2 19 A number of intermediate moisture foods are 0.4 nonea commercially available. Intermediate moisture pet foods Propyl para ben 0.03 19 are a large share of the pet food market. The market for 0.05 19 intermediate moisture foods is expected to continue to Methyl/propyl paraben 0.02 19 0.05 19 grow. Sodium benzoate 0.05 19 0.10 10 REFERENCES Calcium propionate 0.20 nonea 0.30 none a Potassium sorbate 0.10 nonea 1. Acott, K. M. and T. P. Labuza. 1975. Inhibition of Aspergillus 0.30 nonea niger in an intermediate moisture food system. J. Food Sci. Propylene glycol 7.0 nonea 40:137-139. 10.0 nonea 2. Acott, K., A. E. Sloan. and T. P. Labuza. 1976. Evaluation of antimicrobial agents in a microbial challenge study for an 1,3-Butylene glycol nonea 5.0 intermediate moisture dog food. J. Food Sci.41 :541-546. 10.0 nonea 3. Boylan, S. L., K. A. Acott, and T. P. Labuza. 1976. Glycerol 1.5 32 Staphylococcus aureus challenge study in intermediate moisture 6.0 39 food. J. Food Sci. 41:918-921. Polyethylene glycol 600 3.0 32 4. Brockmann. M. C. 1970. Development of intermediate foods for 10.0 33 military use. Food Techno!. 24:896-900. Sorbitol 4.3 32 5. Burrows, L E., and D. Barker. 1976. Intermediate moisture pet 14.3 51 foods. pp. 43-53. In R. Davies, G. G. Birch, and K. H. Parker (eds.) Intermediate moisture foods. Applied Science Publishers, Control 0 19 London. 6. Collins. J. L .. C. C. Chen. J. R. Park, J. 0. Mundt, I. E. McCarty, aNo mold growth by day 51. and M. R. Johnston. 1972. Preliminary studies on some properties

JOURNAL OF FOOD PROTECTION. VOL. 45, APRIL 1982 INTERMEDIATE MOISTURE FOODS 491

of intennediate moisture, deep-fried fish flesh. J. Food Sci. 21. Leistner, L., and W. Rode!. 1976. The stability of intermediate 37:189-190. moisture foods with respect to microorganisms. pp. 120-137. In R. 7. Corry, J. E. L. 1976. The safety of intermediate moisture foods Davies, G. G. Birch and K. J. Parker (eds.) Intermediate Moisture with respect to Salmonella. pp. 215-238. In R. Davies, G. G. Birch Foods. Applied Science Publishers, London. and K. J. Parker (eds.) Intermediate moisture foods. Applied 22. Leung, H., H. A. Morris, A. E. Sloan, and T. P. Labuza. 1976. Science Publication, London. Development of an intennediate-moisture processed cheese food 8. Flink, J. M. 1977. Intermediate Moisture Food Products in the product. Food Techno!. 30(7):42-44. American Marketplace. J. Food Proc. Pres. 1:324-339. 23. Pelaez, J., and M. Karel. 1980. Development and stability of 9. Hardman, T. M. 1976. Measurement of water activity. Critical intermediate moisture tortillas. J. Food Proc. Pres. 4:51-65. appraisal of methods. pp. 75-88. In R. Davies, G. G. Birch and K. 24. Plitman, M., Y. Park, R. Gomez, and A. J. Sinskey. 1973. J. Parker (eds.) Intennediate moisture foods. Applied Science Viability of Staphylococcus aureus in intennediate moisture Publishers, London. meats. J. Food Sci. 38:1004-1008. 10. Harper, J. M. Food extrusion. CRC Crit. Rev. Food Sci. Nutr. 25. Reid, D. S. 1976. Water activity concepts in intermediate 11:155-215. moisture foods. pp. 54-65. In R. Davies, G. G. Birch, and K. J. 11. Heidelbaugh, N.D., and M. Karel. 1975. Intennediate moisture Parker (eds.) Intennediate moisture foods. Applied Science food technology. pp. 619-641. In S. A. Goldblith, L. Rey and W. Publishers, London. W. Rothmayr(eds.) Freeze drying and advanced food technology. 26. Robson, J. N. 1976. Some introductory thoughts on intermediate Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/5/484/1653902/0362-028x-45_5_484.pdf by guest on 27 September 2021 Academic Press, New York. moisture foods. pp. 32-42. In R. Davies, G. G. Birch, and K. J. 12. Kaplow, M. 1970. Commercial development of intermediate Parker (eds.) Intennediate moisture foods. Applied Science moisture foods. Food Techno!. 24:889-893. Publishers, London. 13. Karel, M. 1973. Recent research and development in the field of 27. Rockland, L. B., and S. K. Nishi. 1980. Influence of water activity low-moisture and intennediate-moisture foods. CRC Crit. Rev. of food product quality and stability. Food Techno!. 34(4):42-51, Food Techno!. 3:329-373. 59. 14. Karel, M. 1975. Stability of low and intermediate moisture foods. 28. Scott, W. J. 1957. Water relations of food spoilage micro­ pp. 643-674. ln S. A. Goldblith, L. Rey and W. W. Rothmayt organisms. Adv. Food Res. 7:83-127. (eds.) 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JOURNAL OF FOOD PRO TECTJON, VOL 45, APRIL 1982