An Improved Colorimetric Assay for Bacterial Lipase in Nonfat Dry Milk

A modification of McKellar and Cholette's (1986) colorimetric method for determining lipase activity in reconstituted non-fat dry milk was developed. The method uses the color reaction between Fast Blue BB and the β-naphthol (BN) enzymatically cleaved from β-naphthyl cap-rylate (BNC) as a measure of lipase activity. In the modified method, a solvent system is used to clarify the sample rather than extracting the colored product. This modification allows measurement of total sample lipase by excluding centrifugation. In addition, the modified method has greater sensitivity with equal ease of use.     

Sensory Quality of Nonfat Dry Milk after Long-Term Storage

Nonfat dry milk was stored under various conditions to determine the effects of temperature, packaging, atmospheric gases, and form of milk on the sensory quality of the stored product. Nonfat dry milk was significantly affected by storage temperature during long-term storage. Nonfat dry milk held at 32°C for 6 mo began to develop offflavors and by 24 mo was considered unacceptable when evaluated by a trained sensory panel. After 4-yr storage nonfat dry milk samples stored at 21°C were rated unacceptable by the panelists. Storage at 10°C resulted in minimal flavor changes in 52 mo. After 4-yr storage, nonfat dry milk samples stored in Polybags were statistically less acceptable than samples stored in cans. The form of milk (instant or regular) did not affect the length of time nonfat dry milk could be stored. Unacceptability of samples was due to an oxidized/stale flavor.     

Fractionation of Nonfat Dry Milk Powder into Protein and Lactose Products

Five processes were used to fractionate low heat NDM into a number of products including crude casein, three types of lactalbumin, crude lactose, United States Pharmacopeia-grade lactose, and a partially deproteinated whey product. Regular lactalbumin and crude lactose were produced by process 1 with a total recovery of 91% of starting NDM solids including those obtained from the casein fraction. Process 2 led to the production of both high and low ash lactalbumin and crude lactose, but the total solids recovery was about 10% lower than process 1 due to extra material handling. Both Processes 3 and 4 allowed for the crystallization of crude lactose from condensed whey containing the full protein complement. Process 4 was similar to process 3 except provision was made to return the mother liquor from the United States pharmacopeia lactose preparation back to the starting casein whey; this increased the solids recovery from 91 to 96%. The fifth process was used to purify the crude lactose of processes 1 to 4 for the preparation of United States Pharmacopeia grade lactose.     

Improved Salmonella Species Recovery from Nonfat Dry Milk Pre-enriched Under Reduced Rehydration

Recovery of Salmonella species from nonfat dry milk was performed by the method of the Association of Official Analytical Chemists (AOAC), in which a 25-g sample is rapidly rehydrated in 225 ml of sterile distilled water. Recovery was improved by swirling pre-enriched samples at an initial 1:2 sample/water ratio and diluting 60 min later to a final 1:9 sample/water ratio before incubation at 35°C. In a second improved method, 25-g samples were gently added to 225-ml volumes of sterile distilled water and allowed to soak undisturbed for 60 min at room temperature before incubation. Direct comparison of the AOAC and soak methods showed that 16 and 62 Salmonella-positive samples, respectively, were detected by each of these methods. Sensitivity of the soak method did not decrease during analysis of four 100-g samples or a single 375-g sample as compared with analysis of fifteen individual 25-g samples.     

Effect of Processing Temperature and Storage Time on Nonfat Dry Milk Proteins

Changes in physicochemical properties of pooled nonfat milk preheated to 63°C (I), 74°C (II), and 85°C (III), before spray-drying were examined. Insoluble material from III contained more protein (particularly at reduced pH) and more coagulated protein-lactose aggregates than either I or II. Soluble material from III was practically depleted of whey proteins which were utilized to form complexes stabilized through disulfide bonds. Milk protein micelles from III were heavier (ca 1 × 10¹¹ g/mole) than either I or II. An unsweetened milk-orange juice blend, which was pasteurized at 63°C for 30 min and stored at 4°C, developed a precipitate which contained more protein and pectin, but less sucrose than the supernatant.     

A Rapid Immunoturbidimetric Method for Whey Proteins in Nonfat Dry Milk and Buttermilk

An immunoturbidimetric assay, using antibodies to whole bovine whey, was developed for the rapid screening of whey proteins in nonfat dry milk and buttermilk. Milk samples are heat-treated prior to analysis to denature the whey proteins for a more uniform response to antibodies. Of the whey proteins tested, the assay is most sensitive to bovine serum albumin and the least sensitive to β-lactoglobulin. Precision of the method is about 4% coefficient of variation with a minimum detectable level of 3% whey protein concentrate added to nonfat dry milk. Results are compared with electrophoretic analysis of whey proteins and high performance size exclusion chromatography of the glycomacropeptide from rennet whey.     

Ethanol Extraction of Lactose from Nonfat Dry Milk: Production of Protein Raffinate

The efficiency of extracting lactose from NDM with aqueous ethanol was investigated under conditions where four factors were varied. The experiments were conducted in a complete random block design using three values for each of the variables: ratios of solvent to solids 10:1, 15:1, and 20:1 (wt/wt); solvent ethanol content of 62.4, 72.9, and 84.0% (wt/wt); temperature during extraction of 10, 25, and 50°C; and added divalent metal ion chelator (citrate) in the amount of 0, 10, and 20 mmol/100 g NDM. The results were evaluated statistically using response surface methodology with a multivariate linear regression equation. Optimal extraction efficiency was obtained with high ratio of solvent to solid and low ethanol concentration of the solvent. High temperatures and high citrate concentrations tended to solvate proteins and make separation by filtration difficult. Milk protein with residual lactose of 2 to 4% was obtained using this one-step extraction process under optimal conditions.     

Sensory and Nutritional Quality of Nonfat Dry Milk in Long‐term Residential Storage

ABSTRACT: Twenty samples of regular and instant nonfat dry milk (NFDM) stored up to 29 y in residential locations at ambient conditions in Nr 10 cans were analyzed for sensory and nutritional quality. Overall acceptability hedonic scores varied widely (2.9 to 6.2), but all samples were considered acceptable for use in an emergency situation by most panelists. A 23‐y‐old sample with low oxygen was not significantly different from fresh samples in overall acceptability hedonic scores. There was no difference in overall acceptability between regular and instant NFDM. Amounts of available lysine (1.4 to 2.6 mg/100 g), thiamin (2.7 to 4.0 μg/g), and riboflavin (12.7 to 20.2 μg/g) were not significantly correlated with sample age.     

Effects of Enzyme Modified Soy Protein on Rennet-Induced Reconstituted Nonfat Dry Milk Coagulum Properties

Soy protein was hydrolyzed by trypsin, pepsin and α-chymotrypsin. Effects of adding hydrolyzed soy protein on rennet-induced nonfat milk coagulum texture and syneresis were studied. Pepsin-modified soy protein increased coagulum firmness and syneresis greater than untreated soy protein. Soy protein hydrolyzed with trypsin for 150 min and added to nonfat milk increased coagulum firmness greater than nonfat milk with no soy protein added. Chymotrypsin-modified soy protein acted similarly to the trypsin modified soy protein except the coagulum firmness was less than nonfat milk alone. Soy protein hydrolyzed by trypsin followed by pepsin increased coagulum firmness more than hydrolysis by a single enzyme and was close to nonfat milk without soy protein.     

Economic Value of Milk Components for Fluid Milk,Cheese, Butter,and Nonfat Dry Milk and Responses to Selection

The consequences of genetically and mechanically altering milk composition were investigated. A base price plus a component differential method of payment was shown to be equivalent to the sum of the components of milk yield (carrier, fat, and protein) times their relative economic value. Relative economic values of carrier, fat, and protein were derived for fluid milk. Linear programming models were developed to simulate the movement of milk through cheese and through butter and NDM manufacturing processes. These models were used to estimate the cost of moving milk through the respective plants, and these values were equated to the “breakeven” cost of carrier. New economic values for fat and protein were developed on these respective values of carrier in the cheese, and in the butter and NDM processes. Seven selection and marketing alternatives were investigated to determine the expected differences in economic returns by varying the selection criteria and the end products of value.     

Color of Nonfat Fluid Milk as Affected by Fermentation

Nonfat milks inoculated and fermented with exopolysaccharide and non-exopolysaccharide producing cultures were compared to nonfat, 2% milkfat and whole milk with instrumental and sensory color measurements. L-(whiteness) and a- values (red/greeness) for fermented nonfat milks were higher than nonfat milk. No differences in L-, a-, or b- values (yellow/blueness) were found between milks fermented with exopolysaccharide as compared to non-exopolysaccharide producing strains. A trained sensory panel scored edge and center whiteness of fermented milks whiterthan nonfat milk. Milks fermented with exopolysaccharide producing cultures were scored higher than non-exopolysaccharide producing cultures with respect to edge and center whiteness. Fermentation and exopolysaccharide production may increase visual perception of whiteness in milk.     

Bioavailability of Calcium from Sesame Seeds, Almond Powder, Whole Wheat Bread, Spinach and Nonfat Dry Milk in Rats

Calcium bioavailability (BV) from sesame seeds, almond powder, whole wheat bread, spinach, and nonfat dry milk (NFDM) was compared to calcium BV from a calcium carbonate (CaCO₃)-supplemented control diet using a rat model. When comparing different calcium sources, the relative BV of the products was CaCO₃ (100%), NFDM (100%) whole wheat bread (95%), almond powder (66%), sesame seeds (65%), NFDM and spinach mixture (52%), and spinach (47%). Separate almond, NFDM, and CaCO₃ diets were supplemented with 0.4% ascorbic acid; vitamin C addition had no significant effect on calcium BV.     

Comparative Evaluation of Whey Protein Concentrate, Soy Protein Isolate and Calcium-Reduced Nonfat Dry Milk as Binders in an Emulsion-Type Sausage

The effects of various nonmeat binders on the yield and textural properties of knockwurst, an emulsion-type sausage product, were investigated. Three whey protein concentrate levels, calcium-reduced nonfat dry milk and soy protein isolate and an all-meat control were evaluated. Whey protein concentrate proved to be a viable binder alternative for specific emulsion-type meat products by providing similar stability, textural and sensory attributes in comparison to equal levels of soy protein isolate and calcium-reduced nonfat dry milk.     

Bioavailability of Calcium from Tofu, Tortillas, Nonfat Dry Milk and Mozzarella Cheese in Rats: Effect of Supplemental Ascorbic Acid

Using a rat model, calcium bioavailability (BV) from tofu, tortillas, nonfat dry milk (NFDM) and mozzarella cheese was compared to a control diet supplemented with calcium carbonate (CaCO₃). The above diets were each formulated with and without 0.05% ascorbic acid. When comparing different calcium sources, the relative BV from tofu (107%) was significantly higher (p < 0.05) than from tortillas (93%) or NFDM (95%). Calcium BV from tofu, cheese (105%) and CaCO₃. (100%) was not different. Vitamin C supplementation has no significant effect on calcium BV. Although some differences were noted, overall calcium BV from each of the tested products was excellent.     

酶法水解奶油制备奶味香精的研究

选取了脂肪酶对不同类型的奶油、奶酪和牛奶等进行酶解。在非水介质下水解，得到了奶香浓郁，赋香效果明显的奶味香精。水解时以乙醇或丙酮为溶剂，在pH7．0、50℃下解4h，酶用量为1％～1．5％时得到的奶味香精香气最浓郁。经过感官评定认为此产品香气自然、柔和，可作为调配奶味香精的香基。     

再制奶在干酪生产中的应用

<正> 半个世纪以来,一些鲜奶供应不足的 国家一直在使用再制奶来生产各种类型的干酪。尽管用再制奶生产干酪会受到当地政府法规的限制以及世界乳品价格波动的影响,但为了满足消费者的需求,以这种方法生产干酪在这些国家已经变得不可或缺。这个现象背后的原因是多种多样且不断变化的,如购买力增强,当地居民膳食结构的调整,以及牛奶组分分离和再制技术的进步。     

云南牛干巴加工过程产生物胺的微生物消长规律

目的:分析云南牛干巴加工过程中产生物胺的微生物的消长规律。方法:采用传统工艺加工牛干巴,并于腌制前、腌制中期、腌制后期、成熟1个月、成熟2个月及成熟3个月取样,用选择性培养基对菌落总数和产生物胺微生物:乳酸菌、假单胞菌属和肠杆菌科细菌进行菌落计数。结果:菌落总数在加工过程中先增加后减少,在成熟1个月时达到最大值;乳酸菌、假单胞菌属和肠杆菌科细菌的数量在加工过程中先增加后减少;其中假单胞菌属和肠杆菌科细菌的数量在腌制后期达到最大值,乳酸菌的数量在成熟1个月达到最大值。结论:从数量上来说,乳酸菌是牛干巴加工中的优势菌。