Srinivas Rayaprolu

Electrostatic spraying of organic acids on biofilms formed by E. coli O157:H7 and Salmonella Typhimurium on fresh produce

Electrostatic spraying which has an even and retained surface coverage could be an effective novel technique to completely cover the surface of fresh produce to disrupt biofilm formation by pathogenic bacteria. Spinach leaves and cantaloupe rind were spot-inoculated with a bacterial culture and stored at 8°C for 72h to allow biofilm formation. Among various green fluorescent protein-labeled strains, ED 14 strain of E. coli O157:H7 and SD 10strain of Salmonella Typhimurium had the best attachment based on colony counts. The produce samples were electrostatically sprayed with malic (MA) and lactic (LA) acid solutions alone (1.0/2.0/3.0/4.0% w/v) or in combination (0.5+0.5/1.0+1.0/1.5+1.5/2.0+2.0% w/v) to test for a reduction in the attached bacteria. A combined treatment of LA 2.0% w/v+MA 2.0% w/v had the highest log reduction (CFU/disk) of 4.14 and 3.6 on the attached E. coli strain ED 14 (spinach) and Salmonella strain SD 10 (cantaloupe), respectively. Crystal violet assay demonstrated the disruptive effect of organic acids on biofilms formed by the pathogenic bacteria. Application of electrostatic spray with a combination of malic and lactic acids resulting in a log reduction (CFU/disk) of 3.6 or higher can improve the microbial safety of spinach and cantaloupe by preventing the pathogenic biofilm formation and bacterial growth.

Functional properties and Angiotensin-I converting enzyme inhibitory activity of soy–whey proteins and fractions

Soy proteins when prepared to high purity can confer good functional properties and the whey by-product is a potential source for bioactivity. In this study, we determined the protein, moisture, fiber, solubility, foaming, emulsion properties, as well as Angiotensin-I converting enzyme (ACE-I) inhibitory activity of prepared soy-whey proteins and its fractions. The soy-whey proteins were fractionated into <5, >5, >10, and >50kDa using ultrafiltration. The expanded AACC methods were used to determine protein, moisture, and fiber analyses of the whey and its fractions. Solubility method was conducted to determine the protein solubility profile of the soy-whey and its fractions at varying pHs. Turbidimetric method was used to evaluate emulsifying activity (EA) and emulsion stability (ES). There were significant differences observed in moisture, protein and salt contents between unfractionated, >50kDa and smaller sized fractions. No significant differences were observed with phytic acid and total dietary fiber contents among all samples. The unfractionated whey protein and >50kDa fraction showed better solubility than other fractions. Unfractionated whey protein had the highest foam capacity (42.7mL) while the fraction >5kDa showed the greatest foaming stability (46min). The highest emulsion activity (0.33±0.1) and stability (825.1±45.1) was obtained with the >50kDa fraction while the unfractionated whey protein had the highest ACE-I inhibition activity. The findings indicate that soy-whey protein fraction (>50kDa) had good solubility, emulsion activity and stability, while the unfractionated whey protein exhibited the strongest ACE-I inhibition percentage (19%).

Bioactivity of a Rice Bran-Derived Peptide and its Sensory Evaluation and Storage Stability in Orange Juice.

A pentapeptide prepared from rice bran demonstrated growth inhibition on human lung, liver, breast, and colon cancer cell lines. The objectives of this study were to evaluate the human prostate cancer growth inhibition by the pentapeptide and its 6-mo storage stability by incorporating spray-dried orange juice, and determining sensory acceptability. The pentapeptide showed inhibition of human prostate cancer cells by 45% at 460 μg/mL concentration. When incorporated in spray-dried orange juice, and reconstituted with water and tested, there was an approximately 10% degradation of the peptide at 620 μg/mL concentration under refrigerated conditions over a 6 mo storage period, whereas at ambient temperature the degradation was 30%. Larger degradation was observed when 240 or 460 μg/mL pentapeptide was used. Overall, consumer panelists liked sensory aspect of the reconstituted pentapeptide incorporated orange juice beverage. Also consumer panelists liked the color and mouthfeel attributes, their hedonic impression of flavor attribute was slightly low due to unpalatable bitter note caused by the presence of the peptide. Incorporation of the pentapeptide in spray-dried orange juice has the potential to serve as a functional food ingredient that can offer health benefits to consumers. It is possible that the structural instability can be minimized by encapsulation.