Introduction. Microorganisms of dairy raw materials tend to adhere to the surfaces of processing equipment and form sustainable biofilms, which is a serious issue in the dairy industry. The goal of the present work was to investigate formation of biofilms on a glass surface in static model conditions, and removal of such biofilms by cleaning. Study objects and methods. The study objects were the permeates of skim milk, sweet whey and acid whey, as well as the biofilms formed and washings from glass slides. Biofilms were removed from the glass with detergents used in the dairy industry. Standard methods of determining microbiological and physicochemical properties were used to characterize the permeates. The biofilm structure and morphology of microorganisms participating in biofilm formation were investigated with a light spectroscopy. The efficiency of biofilm removal in a cleaning process was quantified with optical density of washings. Results and discussion. Biofilms in whey permeates formed slower compared to those in skimmed milk permeate during the first 24 h. Yeasts contributed significantly to the biofilm microflora in acid whey permeate throughout 5 days of biofilm growth. Well adhered biofilm layers were the most stable in skimmed milk permeate. The highest growth of both well and poorly adhered biofilm layers was observed in sweet whey permeate after 3–5 days. It was established that the primary attachment of microorganisms to a glass surface occurred within 8 h, mature multicultural biofilms formed within 48 h, and their partial destruction occurred within 72 h. Conclusion. The research results can be used to improve the cleaning equipment procedures in processing secondary dairy raw materials.
Lactulose is a prebiotic that has found a wide application in medicine and food industry. Commercial lactulose is usually synthesized by isomerization in alkaline media at high temperatures. Enzymatic methods offer a more sustainable alternative and require more moderate processing conditions. This review covers 44 years of scientific publications (1978–2022) on the enzymatic synthesis and purification of lactulose. The materials were retrieved from Scopus, Web of Science, PubMed, and Elibrary databases. The enzymatic approach to lactose-to-lactulose conversion has two methods: isomerization (direct) and transgalactosylation (via hydrolysis). Isomerization exploits cellulose-2-epimerases, but their safety status is still rather vague. As a result, cellulose-2-epimerases are not commercial. Epilactose is a by-product of isomerization. Transgalactosylation involves β-galactosidases with an official international safety status (GRAS). It is available on the market, and its action mechanism is well understood. This article systematizes various data on the conditions for obtaining the maximal yields of lactulose by different enzymes. The Kluyveromyces lactis yeast and the Aspergillus oryzae mold are the main sources of β-galactosidases in lactulose production. The yield can reach 30% if the processing conditions are optimal. Fructose remains the main problem in the production process. No scientific publications revealed a direct relationship between the maximal yields of lactulose and the molar fructose-tolactose ratios. Cellobiose epimerases make it possible to achieve high yields of lactulose (70–80%). However, these enzymes are associated with genetic engineering and mutagenesis, which challenges their safety status. The most promising trends in lactulose biotechnology include secondary dairy raw materials, immobilized enzymes, membrane reactors, complex production processes, lactose-to-lactulose conversion, and purification of final product.
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