Compounds with the ability to inhibit angiotensin-converting enzyme (ACE) are used medically to treat human hypertension. The presence of such compounds naturally in food is potentially useful for treating the disease state. The goal of this study was to screen lactic acid bacteria, including species commonly used as dairy starter cultures, for the ability to produce new potent ACE-inhibiting peptides during milk fermentation. Strains of Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus helveticus, Lactobacillus paracasei, Lactococcus lactis, Leuconostoc mesenteroides, and Pediococcus acidilactici were tested in this study. Additionally, a symbiotic consortium of yeast and bacteria, used commercially to produce kombucha tea, was tested. Commercially sterile milk was inoculated with lactic acid bacteria strains and kombucha culture and incubated at 37°C for up to 72 h, and the liberation of ACE-inhibiting compounds during fermentation was monitored. Fermented milk was centrifuged and the supernatant (crude extract) was subjected to ultrafiltration using 3- and 10-kDa cut-off filters. Crude and ultrafiltered extracts were tested for ACE-inhibitory activity. The 10-kDa filtrate resulting from L. casei ATCC 7469 and kombucha culture fermentations (72 h) showed the highest ACE-inhibitory activity. Two-step purification of these filtrates was done using HPLC equipped with a reverse-phase column. Analysis of HPLC-purified fractions by liquid chromatography-mass spectrometry/mass spectrometry identified several new peptides with potent ACE-inhibitory activities. Some of these peptides were synthesized, and their ACE-inhibitory activities were confirmed. Use of organisms producing these unique peptides in food fermentations could contribute positively to human health.

Egyptian cheeses are considered an important part of the Egyptian diet. This study aimed to examine 60 random samples of different types of commercial cheeses in Egypt, including soft cheeses (Domiati and Tallaga) and hard cheeses (Cheddar and Ras). The samples were subjected to chemical and microbial examination. Biogenic amines (BAs) are nitrogenous compounds found in a variety of foods; their presence is undesirable and related to spoilage, and can result in toxicological effects in humans. Thus, BAs were determined by using a high-performance liquid chromatography (HPLC) analysis. Moreover, the ability of Bacillus polymyxa D05-1 to reduce levels of experimentally added biogenic amines during the manufacturing of Tallaga cheese was investigated. The obtained results revealed variations in the chemical composition between the investigated samples. Furthermore, many cheese samples contained high levels of BAs, including histamine, tyramine and putrescine. Domiati cheese had the highest levels of BAs, followed by Tallaga and Cheddar, whereas Ras cheese had the lowest levels. The existence of yeasts, molds, coliforms and the high levels of BAs in cheese samples indicate the unsanitary conditions in which they were made and stored. Furthermore, addition of B. polymyxa D05-1 during Tallaga cheese manufacturing resulted in a reduction in BA levels.

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