A Membrane-Filter Technique to Test for the Significance of Sublethally Injured Bacteria in Retail Pasteurized Milk

1975 ◽  
Vol 38 (2) ◽  
pp. 87-88 ◽  
Author(s):  
T. J. CLAYDON
Keyword(s):  
Shelf Life ◽  
Membrane Filter ◽  
Selective Medium ◽  
Pasteurized Milk ◽  
Filter Technique ◽  
Litmus Milk ◽  
Keeping Quality ◽  
Membrane Transfer

A membrane transfer procedure previously described was used to study the possible role of sublethally injured bacteria in the keeping quality of retail pasteurized milk. Trypticase soy broth (TSB) was used as nonselective medium and TSB plus NaCl at pH 6.0 (TSBS 6.0), as the selective medium inhibitory to injured organisms. In pasteurized milk at early stages of storage, colony counts on the latter medium were much lower than on the former. Subsequent transfer of the TSBS 6.0 filters to fresh TSB and further incubation usually increased the counts to about the initial TSB range. Generally the organisms presumed injured and subsequently recovered were the same types as those considered uninjured. They were mainly streptococci and micrococci that produced only slow changes in litmus milk at 5 C, so they are of doubtful significance in the shelf life of retail milk at refrigerator temperatures.

Effect of oxygen on the keeping quality of milk: II. Effect of available oxygen on bacterial spoilage and oxygen uptake

1982 ◽  
Vol 49 (3) ◽  
pp. 425-437 ◽  
Author(s):  
Monika J. A. Schröder
Keyword(s):  
Oxygen Uptake ◽  
Shelf Life ◽  
Bacterial Growth ◽  
Bacterial Count ◽  
Bacterial Activity ◽  
Pasteurized Milk ◽  
Keeping Quality ◽  
Quality Of Milk ◽  
Effect Of Oxygen

SUMMARYThe effect of limiting the amount of O2 present in commercially pasteurized milk on bacterial growth and on the keeping quality of the milk was investigated. No increase in bacterial count of laboratory pasteurized milk during storage for 9 d at 5 °C was observed and O2 consumption due to bacterial activity was low. In commercial pasteurized milk containing post-pasteurization contamination (PPC) growth of strict aerobes was encouraged by high O2 content while that of coliforms was less dependent on O2 level. The amounts of headspace (HS) O2 consumed in milk with PPC growth were large. Reducing the dissolved O2 content of commercial pasteurized milk stored in O2-impermeable containers without HS had little effect on bacterial activity and shelf-life.

Effect of psychrotrophic post-pasteurization contamination on the keeping quality at 11 and 5 °C of HTST-pasteurized milk in the UK

1982 ◽  
Vol 49 (4) ◽  
pp. 619-630 ◽  
Author(s):  
Monika J. A. Schröder ◽  
Christina M. Cousins ◽  
Charles H. McKinnon
Keyword(s):  
Shelf Life ◽  
Storage Temperature ◽  
Bacterial Counts ◽  
Pasteurized Milk ◽  
Colony Forming Units ◽  
Keeping Quality ◽  
The Uk ◽  
Spoilage Microflora

SummaryThe keeping quality of commercial HTST-pasteurized milk and laboratory pasteurized milk from a common bulk raw supply has been investigated for 5 dairies. Spoilage occurred at levels of total bacterial counts around 107 colony forming units/ml, but with a slightly higher off-flavour threshold for the commercial milks than the laboratory pasteurized milks. The predominant microflora at spoilage and the type of off-flavour produced differed between the 2 types of milk. Raising the storage temperature from 5 to 11 °C caused a slight shift in the spoilage microflora and led to an average reduction in the shelf life of the laboratory pasteurized milk from 28 to 6 d and of the commercial pasteurized milk from 13 to 5 d. Changes in the level of post-pasteurization contamination (PPC) were reflected in changes in keeping quality, particularly at 5 °C. However, the greatest improvements were found in the absence of PPC.

Usefulness of the Benzalkon-Crystal Violet-ATP Method for Predicting the Keeping Quality of Pasteurized Milk

1982 ◽  
Vol 45 (10) ◽  
pp. 928-931 ◽  
Author(s):  
G. M. WAES ◽  
R. G. BOSSUYT
Keyword(s):  
Shelf Life ◽  
Crystal Violet ◽  
Quantitative Estimation ◽  
Bacterial Count ◽  
Total Bacterial Count ◽  
Life Test ◽  
Pasteurized Milk ◽  
Keeping Quality ◽  
Factory Laboratory

Using the benzalkon-crystal violet-ATP method (BC-ATP method), post-pasteurization contamination of pasteurized milk caused by gram-negative bacteria can be determined within 24 h. This study determined to what extent the keeping quality of pasteurized milk can be predicted by applying this BC-ATP method. Results obtained with the BC-ATP method for 100 samples of pasteurized milk were compared with those recorded in the shelf-life test (total bacterial count after 10 d of storage of samples at 7°C; standard: 106 bacteria per ml) and the Moseley test (bacterial count after 5 d of storage at 7°C; standard: 105 bacteria per ml). Using the shelf life test and the Moseley test, 14 and 8% of the results, respectively, did not correspond with those obtained with the BC-ATP method. From the results obtained, it was obvious that the greater the post-pasteurization contamination of the pasteurized milk, the lesser is the keeping quality. A quantitative estimation of the degree of post-pasteurization contamination can be obtained satisfactorily by applying the BC-ATP method to 1000-, 100-, 10- and 1-ml portions. The Moseley test takes too much time to achieve a good coordination between the factory laboratory and the pasteurization and filling sections of the dairy factory. By substituting the BC-ATP method applied to 100-ml portions of pasteurized milk for the Moseley test (5 d at 7°C; standard: 100,000 bacteria per ml) almost the same information is obtained within 24 h.

Comparison between the EC plate count test at 21 °C and an accelerated plate count method for assessing the keeping quality of pasteurized milk

1992 ◽  
Vol 59 (3) ◽  
pp. 431-436 ◽  
Author(s):  
Sarah A. Langford ◽  
Rohan G. Kroll
Keyword(s):  
Plate Count ◽  
Gram Negative ◽  
Rapid Methods ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Commercial Interest ◽  
Count Method ◽  
Keeping Quality ◽  
Plate Count Method

The keeping quality of properly refrigerated pasteurized milk and cream is primarily determined by post-pasteurization contamination by Gram-negative psychrotrophic bacteria (Phillips et al. 1981; Schröder et al. 1982). Reliable and rapid methods of assessing the levels of contamination by these organisms are therefore of commercial interest.

Application of the sensory evaluation method when using the accelerated storage technique

2021 ◽  
pp. 15-17
Author(s):  
Елена Анатольевна Юрова ◽  
Татьяна Викторовна Кобзева
Keyword(s):  
Shelf Life ◽  
Evaluation Method ◽  
Main Task ◽  
Long Term Storage ◽  
Organoleptic Characteristics ◽  
Accelerated Storage ◽  
Shelf Stable

Основной задачей для обеспечения качества функциональных продуктов длительного хранения является наличие методов оценки срока годности, применение которых позволит оценить не только качество продукта, но и его функциональные свойства на протяжении всего срока годности продукта. В настоящее время установлена возможность разработки методики ускоренного хранения для функциональных продуктов на молочной основе длительного хранения с применением метода ASLT и математического моделирования, исходя из имеющихся наработанных статистических данных по показателям окислительной порчи, содержанию свободных аминокислот и параметрам оценки продуктов гидролиза белка. В данной работе приведена оценка роли органолептического анализа при подтверждении срока годности продукции, рассмотрены основные процессы, влияющие на изменение органолептических характеристик при хранении. По результатам выполненной работы даны рекомендации по использованию метода органолептической оценки применительно к функциональным продуктам на молочной основе при использовании методики ускоренного хранения. The main task for ensuring the quality of functional shelf-stable products is the availability of methods for assessing the shelf life, the use of which will allow not only assessing the quality of the product, but also its functional properties throughout the entire shelf life of the product. Currently, the possibility of developing a method of accelerated storage for functional milk-based products for long-term storage using the ASLT method and mathematical modeling has been established, based on the available accumulated statistical data on indicators of oxidative spoilage, the content of free amino acids and parameters for evaluating protein hydrolysis products. This work evaluates the role of organoleptic analysis in confirming the shelf life of products, considers the main processes that affect the change in organoleptic characteristics during storage. Based on the results of the work performed, recommendations were given on the use of the method of organoleptic assessment in relation to functional milk-based products when using the accelerated storage method.

scholarly journals Influence of the microbiological quality of raw milk on the shelf life of pasteurized milk

2019 ◽  
Vol 40 (4) ◽  
pp. 1469
Author(s):  
José Carlos Ribeiro Júnior ◽  
Aline Marangon de Oliveira ◽  
Fernando Godoi Silva ◽  
Lorena Natalino Haber Garcia ◽  
Cátia Maria de Oliveira Lobo ◽  
...  
Keyword(s):  
Shelf Life ◽  
Microbiological Quality ◽  
Raw Milk ◽  
Poor Quality ◽  
Pasteurized Milk ◽  
Microbial Counts ◽  
Legal Standards ◽  
Milk Samples ◽  
Brazilian Standard

The dairy industry strives to produce high quality products with high nutritional value as well as to meet the legal standards for longer shelf life. However, these goals are made unfeasible by the poor quality of raw milk produced in some regions of Brazil. Others Brazilian dairy regions, however, already succeed in producing milk with low microbial counts, such as the municipality of Castro, Paraná state, designated as the ‘Brazilian dairy capital’. In order to evaluate the effect of raw milk quality on microbial counts during the shelf life of pasteurized milk, samples were collected from two dairy regions of Paraná: the northern and Castro region, characterized by milk production with high and low microbiological counts, respectively. Samples were experimentally pasteurized and the total microorganism counts were analyzed for 18 days at 7°C, using the Brazilian standard microbiological count limit for pasteurized milk (8 x 104 CFU/mL) as the end of the shelf life. Low microbiological counts in raw milk (Castro) resulted in significantly lower counts shortly after pasteurization and over the entire shelf life, meeting the pasteurized milk standard for 18 days. The temporal evolution in the counts over 18 days for the milks of high and low microbiological count was similar; however, the disparity between the absolute counts between the regions was significant (p < 0.05). Of the milk samples from northern Paraná, four (44.4%) already had counts higher than that of the legislative limit for pasteurized milk immediately after pasteurization. The others (five) reached the maximum microbiological count limit for pasteurized milk on the 6th day after pasteurization. In contrast, the milk from the Castro region remained below the limit throughout the analysis period. Thus, it can be stated that the microbiological quality of raw milk is directly related to the initial count of microorganisms after pasteurization, and that pasteurized milk produced from raw milk with low microbiological counts complies with the Brazilian legislation for 18 days following thermal processing.

Origins and levels of post pasteurization contamination of milk in the dairy and their effects on keeping quality

1984 ◽  
Vol 51 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Monika J. A. Schröder
Keyword(s):  
Shelf Life ◽  
Considerable Influence ◽  
Gram Negative ◽  
Pasteurized Milk ◽  
Wide Range ◽  
Keeping Quality ◽  
Before And After ◽  
Milk Feeding

SummaryBacterial post pasteurization contamination with psychrotrophic Gram-negative rods (GNR) was measured in commercial milks before and after transfer to retail containers. The tanks of pasteurized milk feeding the filling units contaminated milk less often (39% of samples) but usually at a higher level than the filling units (92% of samples). The number of GNR present had a considerable influence on the shelf life of milk, and the range found in commercially pasteurized milk was reflected in a wide range of shelf lives.

Molecular Analysis of Spoilage-Related Bacteria in Pasteurized Milk during Refrigeration by PCR and Denaturing Gradient Gel Electrophoresis

2009 ◽  
Vol 72 (3) ◽  
pp. 572-577 ◽  
Author(s):  
HONGFEI HE ◽  
JIN DONG ◽  
CHIN NYEAN LEE ◽  
YONG LI
Keyword(s):  
Shelf Life ◽  
Gel Electrophoresis ◽  
Denaturing Gradient Gel Electrophoresis ◽  
Plate Count ◽  
Pasteurized Milk ◽  
Milk Samples ◽  
Gradient Gel Electrophoresis ◽  
Aerobic Plate Count ◽  
Species Specific

Bacterial diversity in fluid milk products has been extensively studied in order to improve milk quality. Here, we illustrate the utility of viable counts and PCR–denaturing gradient gel electrophoresis (DGGE) for monitoring the microbial spoilage of pasteurized milk during shelf life. Five pasteurized milk samples stored at 4°C were examined at 10 and 5 days before expiration and on the expiration day. With bacterial DNA extracted directly from the samples, PCR-DGGE analysis indicated that Pseudomonas became dominant in four samples. Meanwhile, the aerobic plate count of these four samples exceeded the regulatory limit of 20,000 CFU/ml at 5 days before expiration, and the rapid psychrotrophic count markedly surpassed the aerobic plate count on the expiration day. Streptococcus and Buttiauxella spp. were detected in several samples. Sequence analysis of DGGE fragments revealed high diversity among Pseudomonas spp. in the milk samples. P. putida and P. migulae grew to high numbers during refrigerated storage. Further identification of Pseudomonas at the species level was facilitated by PCR and multiplex PCR using species-specific primers; consequently, P. fluorescens and P. fragi were observed. These results highlight an important role of Pseudomonas in the shelf life of pasteurized milk.

Melatonin treatment improves the shelf-life and postharvest quality of table grape (Vitis labrusca L. cv. ‘Fengzao’)

2020 ◽  
Vol 10 (4) ◽  
pp. 665-676
Author(s):  
Ya-Dan Sun ◽  
Da-Long Guo ◽  
Sheng-Di Yang ◽  
He-Cheng Zhang ◽  
Lei-Lei Wang ◽  
...  
Keyword(s):  
Dna Methylation ◽  
Shelf Life ◽  
Soluble Solids ◽  
Postharvest Quality ◽  
Vitis Labrusca ◽  
Physiological Indicators ◽  
Treatment Groups ◽  
Table Grapes

BACKGROUND: Melatonin (MT) is an endogenous indoleamine that regulates senescence progression and stress response in plants. OBJECTIVE: Here, we investigated the effect of MT on the shelf-life and postharvest quality of table grapes (Vitis labrusca L. cv. ‘Fengzao’). METHODS: After harvesting, ‘Fengzao’ grapes were immersed in MT solution at various concentrations (0 [as control], 0.05, 0.1, 0.5 and 1.0 mM for 2 h and stored at 24±1 for 15 days. Physiological indicators including weight loss rate, firmness, contents of total soluble solids (TSSs), ascorbic acid (AsA), malondialdehyde (MDA), hydrogen peroxide (H2O2), and activities of catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) were investigated. Additionally, the DNA methylation rate of ‘Fengzao’ grapes were measured using the methylation-sensitive amplification polymorphism (MSAP) technique. RESULTS: Application of MT effectively delayed grape senescence in all treatment groups compared with the control, with the longest delay observed in the 0.5 mM treatment. Additionally, the rate of DNA methylation decreased in all the 0.5 mM MT treatment groups, indicating a potential role of MT in demethylation. CONCLUSIONS: Our results suggest that the exogenous application of MT can delay the senescence of grapes during postharvest.

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