Effect of organic acid on recovery yields and characteristics of rohu (Labeo rohita) protein isolates extracted using pH shift processing

Utilizing Bullseye fish processing frame waste to produce edible proteins and quality assessment of the recovered proteins

The aim of the study was to utilize the waste generated from Bullseye (Priacanthus hamrur) fish processing to recuperate proteins. Considering the cost-effectiveness, versatility, and color improvement after the pH shift method, proteins from this waste were extracted by the pH shift method using hydrochloric acid and sodium hydroxide. The properties of extracted proteins were studied in detail. During the protein solubility measurement, maximum solubilization was found at pH 3.0 (13.10 mg/mL) on the acidic side and pH 11.0 (14.25 mg/mL) on the alkaline side with a total yield of 51.62 ± 0.23 and 45.42 ± 0.29 (%), respectively. The process variables tested in this study showed a significant effect on protein solubility (p < 0.05). The protein content of the isolates extracted from the waste was 23.80 ± 0.49 and 22.48 ± 0.39% for acid and alkali processed isolates, which was significantly higher than the mince (19.46 ± 0.67%). pH shift processing of Bullseye proteins caused a significant reduction in its pigments, lipids, and myoglobin content (p < 0.05). Proteins extracted using alkali had significantly higher values for foaming stability, water holding capacity, and emulsion capacity than proteins extracted using acid. An overall assessment indicated that protein isolates obtained using alkali extraction were better in terms of textural attributes, gelling ability, and amino acid profile than protein isolates extracted using the acid process.

Utilization of fish protein isolates to supplement oat-based cookies and assessment of end product quality

Bullseye and Pacu fish processing waste were valorized through its conversion into functional protein isolates, followed by the utilization of recovered proteins to supplement oat-based cookies at different levels (0, 2, 4, 6, 8 and 10 g/100 g) and baking temperatures (100, 150, 170, 180, 190 ˚C). With different replacement ratios and baking temperatures, the best selection was made at (4 and 6%) and baking temperatures (160 and 170 ˚C) for BPI (Bullseye protein isolate) and PPI (Pacu protein isolate) based cookies, respectively based on sensory and textural characteristics. The developed products were analyzed for its nutritional, physical, textural, and sensory quality. No significant differences were found in the moisture and ash contents of the cookies from different lots, while the protein content was highest for cookies with 6% PPI. The spread ratio was lower reported for the control cookies compared to the fish protein isolate-based counterpart (p < 0.05), and it decreased with increasing thickness of cookies. Significantly higher total essential amino acid values were obtained in cookies supplemented with 6% Pacu protein isolates, whereas 4% Bullseye protein isolate-supplemented cookies were higher in total non-essential amino acid content. The total plate count was higher in control cookies (0.35 ± 0.33 cfu/g) compared to fish protein isolate-supplemented cookies. The hardness values were maximum for control group cookies (19.14 ± 0.98 N) compared to protein isolate incorporated cookies (17.22 ± 1.05 N and 16.26 ± 0.9 N). However, the difference among the all-treatment group is not significant (p > 0.05).

Synergistic effects of pH shift and heat treatment on solubility, physicochemical and structural properties, and lysinoalanine formation in silkworm pupa protein isolates

The application of silkworm pupa protein isolates (SPPI) in food industry was limited because SPPI's solubility is poor and it contains a potential harmful component of lysinoalanine (LAL) which formed during protein extraction. In this study, combined treatments of pH shift and heating were performed to improve the solubility of SPPI and to reduce the content of LAL. The experimental results showed that the promoting effect on SPPI's solubility by alkaline pH shift + heat treatment was greater than that by acidic pH shift + heat. And an 8.62 times increase of solubility was observed after pH 12.5 + 80 ℃ treatment compared to the control SPPI sample which was extracted at pH 9.0 without pH shift treatment. Very strong positive correlation was found between alkali dosage and SPPI solubility (Pearson's correlation coefficient r = 0.938). SPPI with pH 12.5 shift treatment showed the highest thermal stability. Alkaline pH shift combined with heat treatment altered the micromorphology of SPPI and destroyed the disulfide bonds between macromolecular subunits (72 and 95 kDa), resulting in reduced particle size and increased zeta potential and free sulfhydryl content of the isolates. The fluorescence spectra analysis showed red shifts phenomena with pH increasing and fluorescence intensity increase with temperature increasing, implying the alterations in the tertiary structure of protein. Compared to the control SPPI sample, the amount of LAL reduced by 47.40 %, 50.36 % and 52.39 % using pH 12.5 + 70 ℃, pH 12.5 + 80 ℃ and pH 12.5 + 90 ℃ treatment, respectively. These findings provide fundamental information for the development and application of SPPI in food industry.