| The most common fermented foods worldwide are perhaps the fermented dairyproducts, which are prepared using milk from a variety of animals. Meanwhile, Kefir isless well known than yoghurt, a fermented milk which is familiar to consumers andknown by many different names in different countries.Kefir is traditionally produced by inoculating milk with Kefir grains containinga symbiotic mixture of beneficial microorganisms such as lactic acid bacteria (LAB),yeasts and acetic acid bacteria. The industrial manufacture of Kefir using grains as thestarter culture is very difficult due to the complexity of their microbiologicalcomposition, which varies widely depending on the origin of the grains as well as theirconditions of storage and handling. At the same time, it is difficult to maintain thestability of the microbiological composition of the Kefir grains over time, especiallyduring the production of successive batches. Although commercial Kefir is traditionallymanufactured from cow’s milk, as ewes, goats, or buffalo milk. However, in somecountries, animal milk is scarce, expensive, or minimally consumed due to dietaryconstraints, preferences, or religious customs.The most reasonable way to remedy this situation is the preparation of Kefirusing a vegetable milk source as peanut-milk, which has nutritional benefits for peopleof all ages because of its high protein content; minerals; and essential fatty acids, suchas linoleic and oleic acids. In addition the usage of pure starter cultures containingdefined microbial strains in specific ratios.There are many studies on the microbiological characteristics of Kefir grains.However, information on the quality characteristics of Kefir (finished product) thatoccur during the manufacturing process is scarce. The effects of processing conditionson the quality of Kefir gel prepared using a mixture of peanut/skimmed milk and acommercial starter culture were studied. Kefir samples incubated at24°C for18,22,26and30h were not found to be significantly different from each other in terms ofrheology, texture, syneresis and water holding capacity. Therefore, an optimalfermentation time of18h was used in Kefir preparation. Fermentation ofpeanut/skimmed milk was carried out at different temperatures for18h. A significantimprovement in the quality of the final product was noticed when the incubationtemperature was increased to28°C, which was regarded as the optimal fermentationtemperature. The quality of Kefir samples made with a ratio of10:0and9:1(peanut/skimmed milk) was found to differ significantly from that of Kefir preparedusing other ratios (8:2,7:3,6:4). Hence, the ratio7:3(peanut/skimmed milk) exhibitedan optimal physico-mechanical properties and microstructure of Kefir. The physicochemical properties and sensorial attributes of Kefir productsprepared from peanut-milk only (PMK) and (7/3) peanut/skimmed-milk (70%PMK)were investigated and compared to those of Kefir made from whole-milk (WMK).Storage modulus (G′), loss modulus (G″) and complex viscosity (η*) values of PMKwere significantly higher than those of70%PMK and WMK witch were notsignificantly different from each other. In addition, PMK sample had the lowestadhesiveness and the highest firmness than70%PMK and WMK. However, themineral and amino acid composition as well as total solids contents were high in both70%PMK and WMK compared to PMK where the protein content and the fat levelwere remarkably high. The WHCs of PMK and70%PMK were significantly higherthan that of WMK. Whereas, their susceptibility to syneresis was significantly lowerthan that of WMK. This latest showed higher moisture and ash contents then otherproducts. Furthermore, the organoleptic attributes of70%PMK were closer to those ofWMK which was regarded as control. Concerning organic acids,70%PMK was foundrich in pyruvic and acetic acids, while WMK abounded in lactic, butyric and propionicacids. In general, the amounts of amino acids present in WMK were lower than thoserecorded in both PMK and70%PMK. The micrograph of PMK showed a dense, highlysmall branched structure. The microstructure of70%PMK was near to that of WMKwhere the structure was spongy with regular pore sizes.The microbiological and physicochemical properties of peanut-milk based Kefirduring cold storage were assessed. Results showed that the rheological characteristicsof the peanut-milk based Kefir were significantly affected by the storage time. Inaddition, the firmness and syneresis values were noticed to increase significantlytoward the later days of storage. Peanut-milk based Kefir showed a decrease in pHduring the storage. Concerning the microbial evolution, lactic acid bacteria decreasedbetween7and14days of storage period, while yeast counts remained constant.The antioxidant properties and total soluble phenolic content of peanut-milk andits Kefir product extracts were studied. The antioxidant activity of peanut-milk basedKefir was investigated through scavenging activity of2,2-Diphenyl-1-picrylhydrazyl(DPPH) radicals and reducing power as well as thiocyanate method. Results showedthat the scavenging activity and reducing power of either peanut-milk or peanut-milkbased Kefir increased with increasing concentration. In addition, at low concentration,peanut-milk based Kefir demonstrated a greater DPPH radical-scavenging activity thanunfermented peanut-milk. Similarly, peanut-milk extract exhibited a significantly lowerreducing power than the Kefir product extract. The antioxidant activity of peanut-milkbased Kefir extract was excellent, with its IC50value of DPPH radical scavengingactivity (5.15±0.4mg/ml) being lower than that of peanut-milk extract (7.28±0.5mg/ml). Furthermore, peanut-milk based Kefir expressed more protective effect againstthe peroxidation of linoleic acid, than that of the milk from which it was prepared. Totalsoluble phenolic content in peanut-milk was significantly lower than that inpeanut-milk based Kefir. The applicability of ultrafiltration for the separation and recovery of polyphenolics inpeanut-milk based Kefir was evaluated. The peanut-milk based Kefir extract wasultrafiltrated sequentially using Millipore with different molecular weight (MW) limits:10,5and3KDa. Results showed that the scavenging activity and reducing power ofthe fractions exhibited a dose dependent effect. In addition, the ultrafiltration can beused as a potential technology to recover phenolic antioxidants from peanut-milk basedKefir extract. It clearly improves the phenolic compounds content in retantate fraction2(10-5KDa) where the antioxidant capacity was higher than other fractions.Furthermore, in retentate fraction2(10-5KDa) the soluble phenolic content wassignificantly higher followed by fraction1(≥10KDa). The main phenolic compoundswhich were identified in the fraction2were: Catechin and P-coumaric acid. |
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