Samples Of Nonfat Dry Milk Research Articles

Characterising variances of milk powder and instrumentation for the development of a non-targeted, Raman spectroscopy and chemometrics detection method for the evaluation of authenticity

ABSTRACTThere is a need to develop rapid tools to screen milk products for economically motivated adulteration. An understanding of the physiochemical variability within skim milk powder (SMP) and non-fat dry milk (NFDM) is the key to establishing the natural differences of these commodities prior to the development of non-targeted detection methods. This study explored the sources of variance in 71 commercial SMP and NFDM samples using Raman spectroscopy and principal component analysis (PCA) and characterised the largest number of commercial milk powders acquired from a broad number of international manufacturers. Spectral pre-processing using a gap-segment derivative transformation (gap size = 5, segment width = 9, fourth derivative) in combination with sample normalisation was necessary to reduce the fluorescence background of the milk powder samples. PC scores plots revealed no clear trends for various parameters, including day of analysis, powder type, supplier and processing temperatures, while the largest variance was due to irreproducibility in sample positioning. Significant chemical sources of variances were explained by using the spectral features in the PC loadings plots where four samples from the same manufacturer were determined to likely contain an additional component or lactose anomers, and one additional sample was identified as an outlier and likely containing an adulterant or differing quality components. The variance study discussed herein with this large, diverse set of milk powders holds promise for future use as a non-targeted screening method that could be applied to commercial milk powders.

Application of Fluorescence Spectroscopy for Monitoring Changes in Nonfat Dry Milk During Storage

The objective of this study was to determine if fluorescence spectroscopy could be used to characterize the biochemical characteristics of nonfat dry milk (NDM) caused by manufacturing and storage conditions. Nine low-heat NDM samples were collected from 3 manufacturers and stored at 4 temperatures (4, 22, 35, and 50°C) for 8 wk. The spectra of Maillard products, tryptophan, and riboflavin were recorded and analyzed with principal components analysis. Colorimetric indices L*, a*, and b* were also determined. The before-storage NDM samples collected from each manufacturer had different fluorescent characteristics. Inconsistency was observed for the NDM samples collected from 1 manufacturer, whereas the samples from the other 2 manufacturers displayed consistent fluorescence characteristics. Biochemical reactions, such as Maillard reaction, modification of the tryptophan environment, and degradation of riboflavin occurred during the manufacturing process. For each of the data collections, discrimination of the NDM samples stored at 50°C from the samples stored at 4, 22, and 35°C was observed in the similarity maps. The factor loadings of the first 2 principal components for the fluorescence spectra of the samples before storage were similar to the principal components analysis results of the samples during storage. It appears that similar factors are responsible for the variation in the samples before storage and their changes during storage. Additionally, storage of the samples at 50°C accelerated these reactions. The results demonstrate that front-face fluorescence spectroscopy, coupled with multivariate statistical methods, can be utilized as an analytical technique to monitor variation in NDM samples from different manufacturers and changes during storage.

Volatile flavor components of stored nonfat dry milk.

Nonfat dry milk (NDM) is widely used both as an ingredient in other preparations and for direct consumption. Flavor quality of NDM is a critical parameter because it can directly impact final product quality. Flavors can be formed in NDM during subsequent storage. Identification of compounds responsible for storage-induced flavors is necessary to correlate sensory quality with potential sources of the flavors. Six NDM samples were selected for volatile flavor analysis based on sensory analysis and storage time. Volatile components were extracted by direct solvent extraction/high vacuum distillation. Volatile extracts were separated into neutral/basic and acidic fractions and analyzed by gas chromatography-olfactometry (GCO) and aroma extract dilution analysis (AEDA). A variety of aldehydes, ketones, and free fatty acids were responsible for generation of flavors in stored NDM. The following compounds exhibited high aroma impact by AEDA: 3-(methylthio)propanal (boiled potato); o-aminoacetophenone (corn tortilla); 2,5-dimethyl-4-hydroxy-3(2H)-furanone and 2-methyl-3-hydroxy-4H-pyran-4-one (burnt sugar); butanoic acid (cheesy); pentanoic acid (sweaty); acetic and hexanoic acids (sour/vinegar); octanoic, decanoic, and dodecanoic acids (waxy); p-cresol (cowy/barny); 3-methylindole (fecal); dimethyl trisulfide (cabbage); (E,E)-2,4-decadienal (fried/fatty); furfuryl alcohol (rubber/vitamin); phenylacetic acid (rose-like); and 1-octen-3-one (mushroom).

Development of a fluorogenic probe-based PCR assay for detection of Bacillus cereus in nonfat dry milk.

A fluorogenic probe-based PCR assay was developed and evaluated for its utility in detecting Bacillus cereus in nonfat dry milk. Regions of the hemolysin and cereolysin AB genes from an initial group of two B. cereus isolates and two Bacillus thuringiensis isolates were cloned and sequenced. Three single-base differences in two B. cereus strains were identified in the cereolysin AB gene at nucleotides 866, 875, and 1287, while there were no species-consistent differences found in the hemolysin gene. A fluorogenic probe-based PCR assay was developed which utilizes the 5'-to-3' exonuclease of Taq polymerase, and two fluorogenic probes were evaluated. One fluorogenic probe (cerTAQ-1) was designed to be specific for the nucleotide differences at bases 866 and 875 found in B. cereus. A total of 51 out of 72 B. cereus strains tested positive with the cerTAQ-1 probe, while only 1 out of 5 B. thuringiensis strains tested positive. Sequence analysis of the negative B. cereus strains revealed additional polymorphism found in the cereolysin probe target. A second probe (cerTAQ-2) was designed to account for additional polymorphic sequences found in the cerTAQ-1-negative B. cereus strains. A total of 35 out of 39 B. cereus strains tested positive (including 10 of 14 previously negative strains) with cerTAQ-2, although the assay readout was uniformly lower with this probe than with cerTAQ-1. A PCR assay using cerTAQ-1 was able to detect approximately 58 B. cereus CFU in 1 g of artificially contaminated nonfat dry milk. Forty-three nonfat dry milk samples were tested for the presence of B. cereus with the most-probable-number technique and the fluorogenic PCR assay. Twelve of the 43 samples were contaminated with B. cereus at levels greater than or equal to 43 CFU/g, and all 12 of these samples tested positive with the fluorogenic PCR assay. Of the remaining 31 samples, 12 were B. cereus negative and 19 were contaminated with B. cereus at levels ranging from 3 to 9 CFU/g. All 31 of these samples were negative in the fluorogenic PCR assay. Although not totally inclusive, the PCR-based assay with cerTAQ-1 is able to specifically detect B. cereus in nonfat dry milk.

A MINIATURIZED ENRICHMENT SEROLOGY METHOD FOR RAPID DETECTION of SALMONELLA FROM POULTRY MEAT and REARING FARMS ENVIRONMENT

A miniaturization of the enrichment serology method for the detection of Salmonella was improved in order to make the technique more reliable, cheaper, and faster. the miniaturized method (“Micromethod”) was compared to the Sperber and Deibel's method (“Macromethod”) and with a classical isolation method; 1062 samples including 700 rearing farms environment samples, 247 poultry meat samples, and 115 nonfat dry milk samples were analyzed. Specificity of both enrichment serology methods was about 92–99.4%. Sensitivity of Micromethod was better than that of the Macromethod for the environmental samples (86.8 and 74.1%, respectively) and the poultry meat samples (87.5 and 77.5%, respectively) but was the same for the nonfat dry milk samples (82.5%). the costs of both methods were respectively 0.43 US $ for the Macromethod and 0.20 US $ for the Micromethod. This “Micromethod” could be proposed for the screening of Salmonella positive batches in the food industries.

EFFECTS of GAMMA-IRRADIATION ON THE CONTENTS of THIAMIN, RIBOFLAVIN, AND VITAMIN B-12 IN DAIRY PRODUCTS FOR LOW MICROBIAL DIETS

Frozen dairy products were exposed to 40 kGy (4 Mrad) of cobalt-60 irradiation to sterilize them for the low microbial diets of immunosuppressed patients. In this study, the levels of thiamin, riboflavin, and vitamin B-12 were measured in Cheddar cheese, mozzarella cheese, yogurt bars, ice cream, and nonfat dry milk before and after irradiation at −78°C. There was no significant change in the levels of thiamin, riboflavin, or vitamin B-12 after irradiation. Samples of nonfat dry milk irradiated at three different temperatures (22°, 0 to 5°, or −78°C) sustained no significant loss of thiamin compared to levels in the nonirradiated fresh product. However, in irradiated mozzarella cheese, more thiamin was retained in products irradiated at −78°C than at 0 to 5°C. Irradiation of cheese, yogurt, ice cream, and nonfat dry milk at −78°C appeared to preserve the content of these three B vitamins.

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.

Selenium Content of Nonfat Dry Milk in Various Countries

The study was to compare the selenium content of nonfat dry milk samples of differing geographic origin. Samples from 15 countries (states) were collected and analyzed for selenium by electrothermal atomic absorption spectrometry. The lowest national mean of the samples collected in 1982 to 1983 was 43μg/kg dry matter (Czechoslovakia) and the highest 340μg/kg (United States, North Dakota). The mean of the entire study was 115±80μg/kg and the range 33 to 420μg/kg. The coefficient of variation of the method, estimated by analyzing a blind control sample repeatedly during the study, was 12%. Selenium content of nonfat dry milk varies greatly depending on the geographic origin of the milk. Nevertheless, the range may be less than that for cereals.

Enumeration of Coliforms in Nonfat Dry Milk and Canned Custard by Hydrophobic Grid Membrane Filter Method: Collaborative Study

A collaborative study was conducted in 14 laboratories to evaluate the performance of the hydrophobic grid membrane filter method against the official final action method, 46.016, for enumeration of coliforms in foods. Twelve artificially contaminated samples of nonfat dry milk and canned custard were analyzed by each laboratory. The random errors (S2r) associated with the hydrophobic grid membrane filter method were significantly lower than those of the official method, and the counts obtained by the new method fell within the 95% confidence interval of the reference method. The coliform counts obtained by the hydrophobic grid membrane filter method did not differ significantly from those obtained by the reference method as measured by a 3-way analysis of variance. The new method has been adopted official first action.

Vitamin A and Haylike Flavour in Nonfat Dry Milk and Pasteurized Low Fat Milks

A market survey indicated that 27% of nonfat dry milk samples had vitamin A levels less than the accepted minimum. As the vitamin A levels decreased during storage, the incidence of haylike flavour increased. For pasteurized skim milk, 39% of the samples had vitamin A levels less than the accepted minimum and 22% exhibited slight haylike flavour on or before their expiry date. Dry blending vitamin A beadlets with nonfat dry milk or addition of beadlets at the agglomeration chamber during instantization of nonfat dry milk were the best fortification methods for preventing vitamin A degradation and haylike flavour production. Fortification of nonfat dry milk with vitamin A dissolved in skim milk and butter oil was unsatisfactory. Ascorbic acid acted as an antioxidant in skim milk and prevented degradation of vitamin A during storage. Evacuating fluid skim milk, or flushing it with nitrogen, had virtually no effect on preventing the degradation of vitamin A.

Chemiluminescence Detection of Nitrite in Nonfat Dried Milk Powders

Determination of nitrite in nonfat dry milk powders by chemiluminescence detection was compared with a colorimetric method specifying Griess reagents. The chemiluminescent technique requires no sample preparation, is free from apparent interferences, and is sensitive to 25 ppb nitrite. Statistical analysis shows no difference at P = 0.05 between the colorimetric and chemiluminescent methods, based on the analysis of 16 commercial nonfat dry milk samples.

Pyruvate as an Indicator of Quality in Grading Nonfat Dry Milk

Samples of skim milk and nonfat dry milk (NDM) made from it were collected, paired and tested for pyruvate concentration, [P], and Direct Microscopic count (DMC). The skim milk was tested for Standard Plate Count (SPC) and Psychrotrophic Plate Count (PPC). The geometric average DMC of skim milk was more than three times higher than that of the paired NDM samples. However, [P] of NDM was not significantly different from that of the skim milk. Although [P] of skim milk was poorly correlated with SPC and PPC, r = .31 and .26, respectively, it was relatively well correlated with DMC, r = .64. Data were widely dispersed around the regression line when [P] was ≤ 4.0 mg/L. However, [P] increased rapidly when DMCs were > 106/ml. A limit of 10 mg/L of [P] in NDM reconstituted 1:9 was chosen to represent the current U.S. Department of Agriculture Standard for DMC in NDM. This limit failed to classify about 10% of the samples correctly, assuming that each geometric mean DMC was correct. However, the probability that samples meeting the DMC standard would be rejected by the pyruvate test was quite low and the probability was moderate that samples which would be acceptable by the pyruvate test would be rejected by the DMC. For the latter, 28% of the samples having DMCs of ≥ 107/ml contained < 10 mg/L of pyruvate. No sample having ≥ 10 mg/L of pyruvate had a DMC of ≤ 107/ml. Pyruvate concentration in NDM did not change during storage at 5 or 32°C for 90 days.

Influence of Drying Plant Environment on Salmonellae Contamination of Dry Milk Products

This study was done to correlate incidence of salmonellae found in the dry milk processing plant environment with finished product contamination. Three plants with various histories of environmental salmonellae incidence were chosen for the study. The daily plant samples representing one lot of production were placed in a 1500-g composite in a sterile sample container and submitted to the central analytical laboratory for analysis. Two samples of nonfat dry milk were found to contain salmonellae in 8 continuous months of sampling and testing. In each instance of finished product positive, the environment had at least four positive samples recorded in the routine environmental program during the week or on the day in which the positive product was noted. Repeat tests of the positive product were negative on one lot and confirmed the positive in two of three retests of the other lot. It may be concluded from this study that controlling salmonellae in the dry milk plant environment will effectively preclude finished product contamination since dry milks are produced in essentially closed systems in a process that includes a pasteurization step.

Aflatoxin M1 in Manufactured Dairy Products Produced in the United States in 1979

In a 1979 survey of manufactured dairy products (992 samples of nonfat dry milk, vanilla ice cream, yogurt, Cheddar cheese, and cottage cheese) for aflatoxin M1 contamination, one sample, a cottage cheese, had detectable aflatoxin equivalent to .08ng/ml in the milk from which the product was made. Samples were taken by Food and Drug District inspectors from randomly selected establishments at three times throughout the year. The distribution of sample quotas to each District was weighted to double the representation of establishments in the southern tier of states. The conclusion from this survey is that in a “normal” year aflatoxin M1 should not be in a manufactured dairy product in the United States at a level in excess of that from milk with .1ng aflatoxin M1/ml.

Survey of Fluid and Nonfat Dry Milks for N-Nitrosamines1,2

A limited survey of milk and dairy products was undertaken to determine the presence of volatile N-nitrosamines, a class of compounds carcinogenic to a broad range of animal species. Nitrosamines were detected and quantitated by a gas liquid chromatograph interfaced with a Thermal Energy Analyzer. Detectable N-nitrosodimethylamine, the only nitrosamine found, ranged from .05 ppb for whole milk to .30 ppb for nonfat dry milk. No N-nitrosodimethylamine was detected in raw milk, whereas 11 of 21 samples of pasteurized milk contained apparent N-nitrosodimethylamine at a mean .10 ppb. N-nitrosodimethylamine also was detected, but not confirmed by mass spectrometry, in evaporated and condensed milk with means .32 ppb and .58 ppb and in 9 of 10 nonfat dry milk samples with a mean of 1.69 ppb. Upon reconstitution condensed milk and nonfat dry milk contained N-nitrosodimethylamine comparable to that in pasteurized milk. No N-nitrosodimethylamine was detected in cultured milk products such as buttermilk and yogurt.

Relationship between Ionized Calcium and Curd Tension in Reconstituted Nonfat Dry Milk

Fifty nonfat dry milk samples from throughout the midwest were collected. They consisted of 34 low- and 16 highheat nonfat dry milk samples. The samples were reconstituted with 15g of sample to 150ml of deionized water, and were analyzed for ionized calcium and curd tension. The calcium was analyzed with an Orion calcium ion activity electrode.Ionized calcium had to be 1.5MM or higher to produce a curd tension of at least 18g. High-heat samples had as low as .8mM of Ca++ and an average curd tension of 4 to 5g. Three samples of low-heat powder had .95 to 1.3mM of Ca++ and curd tensions of only I to 4g. When ionized calcium in these samples was adjusted to 2.0mM Ca++ by adding CaCl2, their curd tensions did not increase.

Comparison of Rennet Curd Tension with Undenatured Whey Protein as a Measure of Heat Treatment

Natural variations in rennet curd tension limit its usefulness as a measure of heat treatment to a greater extent than do the natural variatiions found for undenatured whey protein nitrogen. Both are correlated with the effective heat applied as calculated from time and temperature measurements. Similar heat treatments of skimmilk fortified with 3% added low-heat nonfat solids showed no significant changes in regression lines for curd tension and whey protein nitrogen after correction for the added solids. Eighteen samples of nonfat dry milk with known preheat treatments were reconstituted to 11% solids for curd tension and whey protein nitrogen measurements. The regression lines were similar to those of the fresh milks were similar to those of the fresh milks. Curd tension increases more rapidly with total solids than does whey protein nitrogen.

Detection and Identification of Salmonella from Dry Milk: Report of a Collaborative Study

Abstract A method for the detection and identification of Salmonella from dry milk was subjected to collaborative study. A 100 g sample is reconstituted in 1 L distilled water with 2 ml 1% aqueous brilliant green dye, incubated, subcultured in selenite cystine broth and tetrathionate broth, incubated, and streaked on selective plates of brilliant green agar, Salmonella-Shigella agar, and bismuth sulfite agar. After incubation, suspicious colonies can be further identified by biochemical and serological tests. Samples of nonfat dry milk and dry whole milk, some inoculated with Salmonella binza, Salmonella tvorthington, and Citrobacter, were examined by 30 collaborators. Results from 23 of 28 collaborators were in agreement; the method will detect and identify Salmonella from positive nonfat dry milk and dry whole milk. The method is recommended for adoption as official first action.

Comparison of the Dye Binding and Kjeldahl Methods for Protein Analysis of Nonfat Dry Milk and Ice Cream

Abstract Ten samples of nonfat dry milk and five samples of vanilla ice cream mix were analyzed in quadruplicate in seven laboratories for protein content by the dye binding method. Laboratory and laboratory times sample effects were significant at the 0.5% level but the coefficients of variation were 1% or less. Comparison of average results obtained by dye binding to those obtained by Kjeldahl show the former to have sufficient accuracy. Direct analysis of NFDM was found to give essentially the same results as analysis of the reconstituted product. It is recommended that the dye binding methods for protein in nonfat dry milk and ice cream mix be adopted as official first action.

Determination of Nitrate and Nitrite in Milk and Dry Milk Products

A modified spectrophotometric method based on the selective diazotization-coupling reaction has been developed capable of detecting 1ppm nitrite in dry milk products. Nitrate can be determined by the same reaction following quantitative reduction to nitrite with a cadmium column. Zinc hydroxide satisfactorily precipitated the milk fat and protein. Nitrate and nitrite levels have been determined in nonfat dry milk samples prepared on a single pilot plant dryer designed for either indirect (steam) heating or direct (gas) firing with natural gas. Slight increases in nitrate content attributable to gas firing were detected, whereas increases in nitrite were nil. A survey of 30 dry milk samples from 13 commercial plants revealed that products produced by direct-firing contained 1 to 3ppm more nitrate-nitrogen than those produced by indirect heating designs.