Rheological and sensory properties of fish gelatin gels as influenced by agar from Gracilaria tenuistipitata

Agar extracted from Gracilaria tenuistipitata and commercial agars were incorporated into fish gelatin at various levels (0, 5, 10, 15 and 20% gelatin substitution). G. tenuistipitata agar (GA) had lower failure stress (~16 kPa) than commercial agar (CA) (~20 kPa). However, the former showed higher failure strain (~30%) with lower melting temperature (65.9 °C). The critical linear stress and failure stress of agar/gelatin mixed gels increased with increasing agar levels (P < 0.05). At 15 and 20% of agar used, the mixed gels containing CA exhibited higher failure stress than those with added GA (P < 0.05). Two melting points of agar/gelatin mixed gels were observed, corresponding to the melting temperatures of gelatin and agar gels. Nevertheless, the incorporation of agar lowered the likeness score of gelatin gel. Thus, both GA and CA had the impact on rheological property and the selected sensory characteristics of fish gelatin, depending on the level of substitution.     

Comparative study on molecular characteristics of acid soluble collagens from skin and swim bladder of seabass (Lates calcarifer)

Acid soluble collagens (ASCs) from skin and swim bladder of seabass (Lates calcarifer) were isolated and comparatively characterised. Higher yield (28.5%) was obtained for ASC from swim bladder, compared with that from skin (15.8%). ASCs from both skin and swim bladder had the similar protein patterns and were identified to be type I. Both α- and β-chains constituted as major components. Fourier transform infrared (FTIR) spectra revealed that both ASCs were triple helix in structure. ASC from both sources contained glycine as the major amino acid with imino acids (proline and hydroxyproline) of 194–195 residues/1000 residues). Peptide maps of both ASCs digested by chymotrypsin and trypsin showed slight differences, suggesting some differences in their primary structure. The thermal transition temperature of swim bladder ASC (35.02 °C) was slightly higher than its skin counterpart (33.33 °C). Based on zeta potential analysis, ASCs from skin and swim bladder had a net charge of zero at pH 6.46 and 6.64, respectively. Therefore, both the skin and swim bladder of seabass could be used potentially for collagen extraction.     

Transformation and Balance of Cyanogenic Compounds in the Cassava Starch Manufacturing Process

The balance of total cyanogenic compounds and distribution of each compound including bound cyanide, cyanohydrin and free cyanide were evaluated in a cassava starch factory, having a production capacity around 100 t starch per day. The production of starch began with transferring washed roots to the rasper, followed by a series of extractors, separators, dewatering centrifuge and flash dryer, with an average water consumption of 11.4 t per ton dry starch. The total amount of cyanogenic compounds entering the process varied from 28 to 43 kg HCN equivalent per day, depending on the root quality. In roots, 64% of bound cyanide was primarily found and it significantly decreased to 22% after rasping whereas the cyanohydrin content increased from 34% to 62%. Most of cyanogenic compounds, predominantly present as cyanohydrin (55 to 70%), was discharged in liquid and solid wastes, accounting for 92% and 5% of total cyanide in roots, respectively. Only a negligible amount of cyanogenic compounds remained in the starch products, having less than 2 mg HCN equivalent per kilogram dry starch. Typically, water from the separators with 91% total cyanide content was recycled to the root washer before being discharged as wastewater, whereas the liquid from the coarse extractor (43% of total cyanide) was recycled to the rasper. This could cause the accumulation of cyanogen in the process and, therefore, in the finished products. With knowledge of the balance and transformation of cyanogens in starch processing, it is possible to assure the quality of low‐cyanide starch by modifying starch process features such as water circulation and pH adjustment.     

Characteristics of collagen from the skin of clown featherback (Chitala ornata)

Acid soluble collagen (ASC) and pepsin soluble collagen (PSC) from the skin of clown featherback (Chitala ornata) were isolated and characterised. Yields of ASC and PSC were 27.64 and 44.63% (dry weight basis) with total collagen recovery of 82.08%. Both collagens contained glycine as the major amino acid with relatively high content of proline, hydroxyproline and glutamic acid/glutamine. Nevertheless, they had the low content of cysteine, histidine and tryrosine. The collagen was characterised as type I, comprising (α1)₂α2‐heterotrimer. Pepsin‐aided process did not affect triple‐helical structure of PSC as determined by FTIR spectra. Thermal transition temperature of ASC (36.28 °C) was slightly higher than that of PSC (35.23 °C). However, no differences in isoelectric point (5.54–5.68) between ASC and PSC were observed. Therefore, collagen from the skin of clown featherback could be successfully extracted for further applications.     

Influence of humectants on the drying kinetics,water mobility,and moisture sorption isotherm of osmosed air-dried papaya

Papaya slices were sequentially soaked in 40, 50, and 60° Brix sucrose solutions. There was a higher water loss and solids gain when 60° Brix sucrose solution was partially substituted with 10% (w/v) sorbitol, 10% (v/v) glycerol, or invert sugar. The modified Henderson and Pabis model provided the best fit to experimental drying kinetics. Moisture sorption isotherm of all dried papaya, at 30 ± 2°C, was a type III with different curvature, revealing different sugar-binding ability towards water molecules. The Henderson model showed suitable fit to experimental desorption isotherm data. NMR water mobility revealed the better ability of glycerol to bind water than sucrose.