{"id":1146,"date":"2021-07-23T06:20:05","date_gmt":"2021-07-23T06:20:05","guid":{"rendered":"https:\/\/evergep.com\/?p=1146"},"modified":"2021-07-27T07:36:19","modified_gmt":"2021-07-27T07:36:19","slug":"optimization-of-uv-c-processing-of-donkey-milk-an-alternative-to-pasteurization","status":"publish","type":"post","link":"https:\/\/evergep.com\/optimization-of-uv-c-processing-of-donkey-milk-an-alternative-to-pasteurization\/","title":{"rendered":"Optimization of UV-C Processing of Donkey Milk: An Alternative to Pasteurization?"},"content":{"rendered":"\n
Dairy Science and Technology, Department of Agricultural Sciences Biotechnology and Food Science, Cyprus University of Technology, 3036 Limassol, Cyprus
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Donkey milk has received much interest lately due to its chemical composition, which is very close to human milk as well as to its unique functional properties (antibacterial, antioxidant, immunomodulatory, and antitumor activities). Furthermore, donkey milk is considered a valid alternative milk for infants and adults suffering from cow milk protein allergy. However, it is recommended by pediatricians and clinicians that raw donkey milk must be thermally processed to render it safe for sensitive population (i.e., infants and immunocompromised). On the other hand, thermal processing is known to reduce the bioactivity of milk. Consequently, the objective of this study is to determine the feasibility of the UV-C system to inactivate or reduce foodborne pathogens in raw donkey milk in order to produce a safe, non-thermally processed donkey milk that can be consumed by special population groups (infants, elderly, immunocompromised). Results obtained from this study indicate that UV-C has the potential to be used as a non-thermal treatment to reduce food borne pathogens present in raw donkey milk<\/p>\n\n\n\n
The effect of UV-C light technology on the inactivation of six foodborne pathogens inoculated in raw donkey milk was evaluated. Fresh raw donkey milk was artificially inoculated with the following foodborne pathogens\u2014L. inoccua<\/em> (NCTC 11288), S. aureus<\/em> (NCTC 6571), B. cereus<\/em> (NCTC 7464), Cronobacter sakazakii<\/em> (NCTC 11467), E. coli<\/em> (NCTC 9001), Salmonella enteritidis<\/em> (NCTC 6676)\u2014and then treated with UV-C doses of up to 1300 J\/L. L. innocua<\/em> was the most UV-C-resistant of the bacteria tested, requiring 1100 J\/L for complete inactivation, while the rest of the bacteria tested was destructed in the range of 200\u2013600 J\/L. Results obtained from this study indicate that UV-C light technology has the potential to be used as a non-thermal processing method for the reduction of spoilage bacteria and foodborne pathogens that can be present in raw donkey milk.Keywords: <\/em>donkey milk<\/a>; UV-C technology<\/a>; non-thermal methods<\/a>; microbial inactivation<\/a>; milk pathogens<\/a><\/p>\n\n\n\n In recent years, there has been a growing interest for donkey milk production and commercialization due to its similar composition with human milk, making it ideal for consumption by sensitive population groups such as infants with cow milk protein allergy (CMPA), the immunocompromised, and the elderly [1<\/a>]. According to the literature, raw donkey milk has a low total bacterial count; nevertheless, the presence of foodborne pathogens such as E. coli 0157<\/em>, S. aureus<\/em>, Campylobacter<\/em> spp., and Cronobacter sakazaki<\/em> was also detected [2<\/a>,3<\/a>,4<\/a>,5<\/a>]. Therefore, raw donkey milk is subjected to thermal pasteurization in order to ensure its microbiological safety and to comply with the European Community Regulation 853\/2004. However, the method has many drawbacks such as high energy cost, and it may influence protein denaturation, deterioration of the technological properties of milk (e.g., prolong enzymatic milk protein coagulation) and loss of nutrients, which is associated with flavor degradation. Thus, there is an interest for alternative methods that would ensure the microbiological safety of the milk while preserving its high biological value. UV-C light technology can be used as an alternative non-thermal method.Ultraviolet light (UV-C) treatment is one of the most promising non-thermal technologies to destruct microorganisms in milk without involving heat [6<\/a>,7<\/a>,8<\/a>,9<\/a>,10<\/a>,11<\/a>,12<\/a>,13<\/a>,14<\/a>,15<\/a>,16<\/a>]. UV technology has the advantage over thermal pasteurization of its ability to minimize the loss of flavors and nutrients, and it is more energy efficient. A limitation of UV-C light processing of milk is its ability to penetrate into opaque liquids resulting in no or very low microbial inactivation [17<\/a>]. Therefore, a strategy to increase the penetration is the use of turbulent flow reactors so that liquid foods are exposed to UV light uniformly.UV radiation covers part of the electromagnetic spectrum in the range of 100\u2013400 nm, which is categorized into three ranges based on their photochemical propertied and biological effects: UV-A (315\u2013400 nm), UV-B (280\u2013315 nm), and UV-C (200\u2013280 nm) [6<\/a>,18<\/a>]. Microbial inactivation from UV light is associated with photochemical changes that take place in proteins and nucleic acids within the cell membrane when UV light is absorbed by the food during UV-C treatment. Photons interact with thymine and cystine nucleoside bases, causing the formation of cross-linked photoproducts, especially cyclobutyl pyrimidine dimers (CPD), which disrupt the DNA transcription, translation, and replication processes that lead to the loss of microbial cell functions and ultimately to cell death of the microorganism [18<\/a>,19<\/a>]. The UV-C light, in particular the wavelength range 250\u2013260 nm, has optimal properties for the inactivation of bacteria, yeast, bacterial spores, molds, and viruses and is most widely used in the food processing industry [10<\/a>].The objective of this study was to determine the feasibility of a continuous UV-C system to inactivate or reduce foodborne pathogens that were artificially inoculated in raw donkey milk compared to the conventional pasteurization process.<\/p>\n\n\n\n Milk samples were collected from the \u201cGolden Donkeys Farm\u201d, located in Larnaca district, Cyprus. All donkeys were fed the same diet consisting of hay, barley, corn, and a concentrate of minerals, vitamins, and salt following the European Directive 98\/58\/EC. Donkeys were healthy, and no antibiotics were administrated prior to sampling. The process of milking was carried out in the stable, and donkeys were milked manually from the same milker. During milking, the udder was cleaned using sterile wet wipes and the nipples using 70% ethanol and dried with sterile gauze. Sampling for microbiological and physicochemical analysis was conducted weekly (33 weeks) from October of 2018 until May 2019 from the daily milk batch (20 L from 20\u201325 milking donkeys). The donkey milk samples were collected in sterilized containers (250 mL), placed in cool-boxes, and transported to the laboratory (4 \u00b0C) and processed during the same working day for physicochemical and microbiological analysis. These 33 samples were used to assess the general microbiological quality of raw donkey milk.For the UV-C and pasteurization experiments, three batches of 7 L donkey milk samples were collected as described above. The initial background flora of the raw milk was assessed each time before subsequent inoculation and processing (UV-C or pasteurization) by serial dilutions in saline solution. A series of dilutions were pour plated in duplicate on Plate Count Agar, and the plates were incubated at 30 \u00b0C for 72 h.<\/p>\n\n\n\n All strains were obtained from National Collection<\/em> of Type Cultures (NCTC). L. inoccua<\/em> (NCTC 11288), S. aureus<\/em> (NCTC 6571), B. cereus<\/em> (NCTC 7464), Cronobacter sakazakii<\/em> (NCTC 11467), E. coli<\/em> (NCTC 9001), and Salmonella enteritidis<\/em> (NCTC 6676) were reconstituted and growth at 37 \u00b0C in brain heart infusion (BHI) broth. All cultures were stored in glycerol (20% vol\/vol) at \u221280 \u00b0C until use. The selection of the above pathogens was based on the fact that these are the main foodborne pathogens associated with milk and dairy products contamination. Moreover, B. cereus<\/em> is a Gram-positive spore-forming bacterium that is capable of surviving pasteurization temperatures, while Cronobacter sakazakii<\/em> has been mainly isolated from dried infant formula, and also, both strains has been previously isolated from raw donkey milk [3<\/a>]. Therefore, the selection of the above strains was based on the future applications of this study, which is the production of a UV-C freeze-dried donkey milk powder and also taking into account the main target group of consumers (i.e., infants, immunocompromised, and the elderly).<\/p>\n\n\n\n To determine the log reduction capability of UV-C and pasteurization treatments, raw donkey milk samples were artificially inoculated with a cocktail of the above bacterial strains at a final concentration of approximately 5 log CFU\/mL. Fresh overnight cultures of all the strains were added directly to donkey milk (7 L) and mixed for 5 min. After 5 min, 500 mL of the artificially inoculated raw donkey milk was placed into a beaker to be used for the pasteurization experiment. Background populations of the pathogens mentioned above were not detected in donkey milk samples prior to inoculation.<\/p>\n\n\n\n1. Introduction<\/h2>\n\n\n\n
2. Materials and Methods<\/h2>\n\n\n\n
2.1. Collection of Milk Samples<\/h4>\n\n\n\n
2.2. Bacterial Strains<\/h4>\n\n\n\n
2.3. Growth of Bacterial Strains and Milk Inoculation<\/h4>\n\n\n\n
2.4. UV-C Processing of Artificially Contaminated Raw Donkey Milk<\/h4>\n\n\n\n