| Abstract: |
Two legume proteins (soybean and chickpea proteins) were isolated and esterified with methanol in the presence of hydrochloric acid (50 mol acid/mole carboxylic group) for 10 h at 4 ˚C to give yields of 83% and 85%, respectively. The Native-PAGE and SDS–PAGE molecular weight distribution of proteins showed slight increments after esterification. Urea-PAGE of native and esterified legume proteins represented exchanges in charge between native and modified proteins. Esterification raised the pIs (iso-electric points) of legume proteins from pH 4.5 for the native legume proteins to pH 8 for esterified proteins. Two esterified legume proteins were tested for their action on these two bacteria against Listeria monocytogenes and Salmonella Enteritidis. Minimum inhibitory concentration (MIC) of methylated soybean protein (MSP) and methylated chickpea protein (MCP) was 100 µg/mL against the two bacteria. The IC50% of the two proteins was 17 µg/mL against 16 µg/mL for penicillin. Higher action of the two proteins was noticed against S. Enteritidis (G-) with IC50% of 15 µg/mL against 85 µg/mL for penicillin. MIC of the two proteins could inhibit the growth of L. monocytogenes and Salmonella Enteritidis by about 97% and 90% after 6-12 h of incubation at 37◦C, respectively. Transmission electron microscopy (TEM) images of the protein-treated bacteria showed various signs of cellular deformation indicating their direct disruptive action on the cell wall and cell membrane on the opposite of penicillin which mainly affects the cell wall biosynthesis.Supplementation of raw milk with 0.5% MSP or MCP could delay its spoilage at room temperature (25˚C) and extend its technological validity up to 12 h instead of 6h. Titratable acidity and pH reached respective levels of 0.22 (as lactic acid %) and 6.30 in raw milk provided with 0.5% esterified legume protein after 12 h of storage at room temperature against 0.49 (as lactic acid %) and 4.64 in case of non-supplemented raw milk. Esterified proteins delayed casein complete degradation to the 24th h instead of 12 h in case of control. Untreated raw milk was the earliest coagulated by alcohol and boiling, i.e. after only 6 h while milk samples provided with 0.5% MSP or MCP were both stable to heat and ethanol treatment up to 12 h of storage at room temperature. Total mesophilic bacteria, Pseudomonas spp. and Enterobacteriaceae counts in MSP and MCP supplemented raw milk were lower by about 1.6-2.0 log as compared to the untreated raw milk after 12h of storage at room temperature. Raw milk technological characteristics were maintained after 12 h of room temperature storage when provided with 0.5% MSP or MCP.MSP and MCP were tested for their potential toxicity when administrated to Wistar Albino rats as one single dose (2,500, 5,000 and 10,000 mg/kg body weight) or repeated daily dose (500 and 2,500 mg/kg body weight/day) for 28 days to disclose the possible toxicity hazards. Single acute administration of very high doses (2,500, 5,000 and 10,000 mg/kg body weight) of MSP and MCP did not produce any death indicating that the NOAEL (Not Observed Adverse Effect Level) of MSP and MCP is more than 10,000 mg/kg body weight/day. Changes in body weight, organ weight, hematological parameters, histo-pathological images of all organs, serum albumin, globulin and albumin/globulin ratio were all within normal amounts in the rats fed with these two methylated proteins and neither significantly different from controls nor dose-dependent. The levels of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), creatinine and urea were rather reduced by the administration of both modified proteins indicating the absence of any adverse effect on hepatic or renal functions.
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