The current industrial practice of using chemical bleach to achieve the pure white colour of agar is deleterious to both human and environmental health. This study evaluates the potential of solar irradiation as an alternative bleaching process for agar extracted from Gracilariopsis heteroclada in Iloilo, Philippines. The physico-chemical properties of agar obtained from alkaline-treated seaweed after exposure to different bleaching conditions (e.g. solar irradiation, hypochlorite solution, and ultraviolet and fluorescent lights) were examined and compared with commercial bacteriological agar. Photobleaching through solar irradiation produced agar with superior gel strength (1038.61 g cm⁻²), high 3,6-anhydrogalactose content (41.44%) and low total inorganic sulphate content (1.87%) without compromising agar yield (19.37%). Solar irradiation offers very promising results as a simple, low-cost, environmentally friendly alternative to the chlorine bleaching process for agar extraction.

Agar is a strongly gelling polysaccharide extracted from gracilarioids, which is processed through conventional alkaline pre-treatment and chemical bleaching. However, the use of chemical bleaching agents has associated health risks to humans and the environment. The aim of the present study was to determine the effects of photo-bleaching in combination with NaOH pre-treatments at 5, 10 and 15% concentrations on the physico-chemical properties of agar extracted from Gracilariopsis heteroclada. The results highlighted that the gel strength of photo-bleached agar extracts PBA-15 (1822.00 g cm⁻²), PBA-10 (1465.60 g cm⁻²), and PBA-5 (1067.70 g cm⁻²) were significantly higher than in either a commercially sourced agar reference sample (756.20 g cm⁻²) or a chemically bleached agar (390.94 g cm⁻²). The physico-chemical properties of PBA extracts fell within the acceptable limits of food-grade agar. Photo-bleached agar extracts (PBA-5, PBA-10, PBA-15) also exhibited a higher lightness (L*) and whiteness index (WI) which makes these agars ideal for microbiological use. This study demonstrated that photo-bleaching by solar irradiation improved the physico-chemical properties of agar from G. heteroclada without the use of a chemical bleaching agent.

In this study, the effects of different washing cycles on the physico-chemical and sensory properties of surimi from Brama orcini were determined. The isolated muscle from B. orcini was divided into five different treatment lots, WC0 (minced, no washing), WC1 (washing cycle 1), WC2 (washing cycle 2), WC3 (washing cycle 3), and WC4 (washing cycle 4) as washing cycle treatments. Both washed and unwashed samples have been added with cryoprotectants and analysed for physico-chemical and sensory evaluation. Results in this study highlighted that increased washing cycle (WC) improved the waterholding capacity of WC3 (88.89%) and WC4 (86.11%) samples, as compared WC0 (63.84%), WC1 (73.51%), WC2 (82.82%) samples (p<0.05). Three to four washing cycles (WC3, WC4) also favoured a significant reduction in the total ash levels (0.50, 0.45%), increased moisture content (71.5, 74.39%), decreased expressible drip losses (11.11, 13.89%), improved whiteness indices (52.46, 51.74%), and increased product over-all acceptability scores (7.12, 8.44) in surimi without compromising its yield (32.00, 31.23%) and total protein content (22.15, 20.84%). This study suggested that washing three times with cold saltwater (10-15°C) improved the physico-chemical and sensory properties of surimi from B. orcini.

Green mussel (Perna viridis) is an extensively cultured bivalve species in the Philippines and a cheap source of valuable nutrients such as essential amino acids and minerals. Experimental samples were prepared by mixing salt to varying mussel meat ratios (1:3, 1:5, 1:7, and 1:9) which were assessed for changes in pH, degree of hydrolysis, and antioxidant activities during fermentation for 30 d. The pH levels in treatments 1:3, 1:5, and 1:7 decreased to low-acid levels (< pH 4.6) as fermentation progressed. Meanwhile, treatment 1:9 did not significantly change from its initial pH level with a slight decrease noted during 15 d but significantly increased at slightly neutral pH level (at 7.22) on 30 d. Formaldehyde nitrogen (formol-N) and the simultaneous formation of ammonia-N significantly increased (p < 0.05) with prolonged fermentation time but were more pronounced in 1:7 and 1:9 treatments. The gradual increase in pH and formol-N in treatments 1:3 and 1:5 could be due to the high salt content at 23.63 ± 0.29 %, and 19.48 ± 0.88 %, respectively, which could have slowed down proteolytic enzyme activity. However, continuous increase in ammonia-N in treatment 1:9 significantly reduced (p < 0.05) amino-N content which lowers the nutritional quality of fermented products. The development of antioxidant activities such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity, ferric reducing antioxidant power (FRAP), and total phenol content (TPC) as gallic acid equivalent (GAE) was highest in treatments 1:7 and 1:9. These findings could be attributed to the increasing degree of protein breakdown producing substances and reaction products with increased bioactivity. This is also supported by the significant positive linear correlation between formol-N and antioxidant system assays (DPPH, FRAP, and TPC) (p < 0.01)

Tuna is abundant in the Philippines, but the by-products during processing in various forms may be a source of waste and environmental pollution. To minimize these wastes, they are utilized directly or fermented to serve as food for humans and animals and as a functional food ingredient since they are rich in proteins and polyunsaturated lipids. For this purpose, they are often converted into protein hydrolysates using proteolytic enzymes. This study optimized the hydrolysis of the yellowfin tuna (Thunnus albacares) viscera (YFTV) using the enzyme neutrase to produce hydrolysates with a high degree of hydrolysis (DH) and foaming capacity (FC). Using the central composite design of the Response Surface Methodology (RSM), the YFTV protein hydrolysis at varying concentrations (0.5-1.5%, w/v) and hydrolysis time (60 to 180 min) was carried out. From the RSM-generated model, the optimum conditions to obtain the highest DH was 179.50 min hydrolysis time and 1.5% enzyme concentration, and for the highest FC, 176.58 hydrolysis time and 1.5% enzyme concentration. The predicted optimum values using the generated linear and quadratic equations were 17.26% DH and 1.60% FC. The lack of a fit test for both responses yielded an insignificant value (p > 0.05) for the model, suggesting that the regression coefficient was sufficient for estimating both responses under any group of variables. The optimized protein hydrolysis conditions of YFTV using Neutrase could be applied in food production systems, especially downstream processing. Furthermore, the utilization of tuna viscera as protein hydrolysates could potentially contribute to the waste management of these processing by-products.

Agar, a phycocolloid naturally extracted from Gracilariopsis heteroclada is strongly influenced by salinity. Wild stocks of G. heteroclada were exposed to varying salinities (20, 30, 40, 50, 60) for 6 days, and subsequently processed for agar extraction using 5 % NaOH. The extracted agar was evaluated regarding yield, gel rheology, colour composition, chemical properties, and infrared spectra. Results highlighted that hypersaline conditions (salinity 50) could produce high agar yield (4.77 %) and viscosity (10.67 mPa s), while agar samples at salinity 40 exhibited gels with high cohesiveness (6.35 mm), gel breaking strength (3.01 N), and gel strength (390.61 g cm⁻²) while having a rather high 3,6-anhydrogalactose content (7.49 %). All samples exhibited FTIR signature peaks at 930 cm⁻¹, confirming the identity of extracted agar from G. heteroclada. Exposure at increasing hypersalinity increased the sulphate levels of agar from G. heteroclada, which implies synthesis of sulphated polysaccharides. Moreover, high 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities were obtained in acid hydrolysed agars at salinities of 40 (74.09 %) and 50 (75.57 %), suggesting that G. heteroclada agars from hypersaline conditions potentially offer antioxidative roles beyond its traditional food use.