Effects of high hydrostatic pressure on antimicrobial protein stability and the rheological and shelf-life properties of donkey milk.

The effects of high hydrostatic pressure (HHP) and heat treatments on antimicrobial protein stability and on the physico-chemical, microbiological, rheological and shelf-life properties of donkey milk were investigated. Although heat treatment at 75°C for 2 min resulted in 1.50 log CFU ml-1 microbial inactivation, losses in activities of lysozyme (58%) and lactoferrin (82%) were observed due to whey protein denaturation. By contrast, HHP application at 400 MPa caused lower enzyme activity losses (22 and 37% respectively) whilst maintaining a significant reduction of microbial load (1.80 log CFU ml-1). Color analyses showed that the lightness values of all samples decreased during storage. Higher flow consistency (viscosity) and lower flow behavior indexes were observed in heat-treated samples compared to untreated and HHP-treated ones, which can be explained by advanced protein denaturation during heat-treatment. The results suggest that HHP is a more suitable process than heat treatment for preservation of donkey milk within the conditions studied.

Use of yeast isolates of cheese origin as adjunct culture in Beyaz cheese: Influence on sensorial, textural and quality characteristics.

The effects of various yeast species isolated from raw-milk cheese were evaluated in Beyaz cheese. Four batches of cheeses were produced, in which the control cheese involved only commercial starter culture while YL, DH and KL cheeses were produced with the incorporation of individual Yarrowia lipolytica, Debaryomyces hansenii and Kluyveromyces lactis, respectively. The chemical composition, microbial counts, sensory attributes, volatile compounds and textural properties of cheeses were determined on days 1, 30, and 60 during the ripening period. The results obtained demonstrated that chemical, microbial and sensory properties of cheese varied depending on yeast species. The cheese with Y. lipolytica was the most preferred and it contained more short chain fatty acids, particularly butyric acid. This result could be due to the higher fat content and advanced lipolytic activity. The ripening index of DH was found to be higher than the other cheeses, showing an advanced proteolytic activity in relation to lower hardness in the texture profile. K. lactis was associated with lactose metabolism and promoted the development of Lactococcus spp. The results highlighted a potential use of yeasts as adjunct cultures in Beyaz cheese to develop the sensory properties such as texture and flavor. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-023-05791-3.

Use of kefir and buttermilk to produce an innovative quark cheese.

Quark cheese is a fermented soft fresh cheese categorised under acid-rennet coagulated cheeses. In this study, alternative raw materials such as kefir and yayik buttermilk were used to produce Quark cheese in comparison with the cheese produced by the acidification of skim milk with mesophilic lactic culture. Samples were kept individually under 35 °C and 100 °C for coagulum formation. Obtained cheeses, were evaluated in terms of some physicochemical, microbiological and sensorial properties in addition to the volatile and peptide profiles. Quark produced from kefir and buttermilk was determined to have preferred properties directly affect the cheese characteristics.

Effect of inulin polymerization degree on various properties of synbiotic fermented milk including Lactobacillus acidophilus La-5 and Bifidobacterium animalis Bb-12.

The effects of inulin degree of polymerization (DP) on the viabilities of Lactobacillus acidophilus La-5 and Bifidobacterium animalis Bb-12 and on some parameters of fermented milk, such as microbiological, rheological, biochemical, and sensory properties, were investigated during 30 d of storage. Samples were produced using L. acidophilus La-5 and B. animalis Bb-12, along with inulin having different DP as prebiotic, and the effects of high-DP (DP ≥ 23) and low-DP (DP ≤ 10) inulin on fermented milk, were determined. The viability of both strains increased when they were used with inulin having any DP. The addition of inulin increased the consistency index of all samples. During storage, we observed an increase in lactic and acetic acid contents of samples in which high-DP inulin was used, for both strains of bacteria. Of the combinations we tested, the sample produced with L. acidophilus La-5 and high-DP inulin demonstrated the highest rheological and sensory performance as well as the best viability of probiotics.

Evaluation of autochthonous Lactococcus lactis subsp. lactis strain as a candidate starter culture in white-brined cheese.

Lactococcus lactis subsp. lactis NCCB100539 isolated from an artisanal raw ewe's milk cheese was evaluated as a potential starter culture in white-brined cheese. As a safety criteria, the cytotoxicity of the viable and heat-killed cells and CFE of this strain were determined on Caco-2 cell line by MTT assay. The antibiotic sensitivity of the strain to nine different antibiotics was also investigated. Cheeses produced using this strain were compared with control cheese in terms of physicochemical, microbiological, sensory properties as well as the peptide and volatile profiles during the 90-days of ripening period. Experimental cheeses had more extensive proteolysis as well as higher sensory scores. Incorporated L. lactis also led to an improvement in the microbial cheese quality. Neither living nor the dead cells and CFE of the strain showed cytotoxicity on Caco-2 cells. Therefore, L. lactis NCCB100539 strain could be a good starter candidate for the industrial white-brined cheeses. Supplementary Information: The online version contains supplementary material available at 10.1007/s10068-023-01332-y.

Protease and lipase activities of fungal and bacterial strains derived from an artisanal raw ewe's milk cheese.

We previously identified the microbiota present during cheese ripening and observed high protease and lipase activity in Divle Cave cheese. To determine the contribution of individual isolates to enzyme activities, we investigated a range of species representing this microbiota for their proteolytic and lipolytic ability. In total, 17 fungal, 5 yeast and 18 bacterial strains, previously isolated from Divle Cave cheese, were assessed. Qualitative protease and lipase activities were performed on skim-milk agar and spirit-blue lipase agar, respectively, and resulted in a selection of strains for quantitative assays. For the quantitative assays, the strains were grown on minimal medium containing irradiated Divle Cave cheese, obtained from the first day of ripening. Out of 16 selected filamentous fungi, Penicillium brevicompactum, Penicillium cavernicola and Penicillium olsonii showed the highest protease activity, while Mucor racemosus was the best lipase producer. Yarrowia lipolytica was the best performing yeast with respect to protease and lipase activity. From the 18 bacterial strains, 14 and 11 strains, respectively showed protease and lipase activity in agar plates. Micrococcus luteus, Bacillus stratosphericus, Brevibacterium antiquum, Psychrobacter glacincola and Pseudomonas proteolytica displayed the highest protease and lipase activity. The proteases of yeast and filamentous fungi were identified as mainly aspartic protease by specific inhibition with Pepstatin A, whereas inhibition by PMSF (phenylmethylsulfonyl fluoride) indicated that most bacterial enzymes belong to serine type protease. Our results demonstrate that aspartic proteases, which usually have high milk clotting activity, are predominantly derived from fungal strains, and therefore fungal enzymes appear to be more suitable for use in the cheese industry. Microbial enzymes studied in this research might be alternatives for rennin (chymosin) from animal source because of their low cost and stable availability. Future studies will aim to purify these enzymes to test their suitability for use in similar artisanal cheeses or in large scale commercial cheeses.