Molecular structure and linear-non linear rheology relation of rice starch during milky, dough, and mature stages.

Immature rice has potential to be used as healthy food. The relation between molecular structure and rheological properties was investigated. The lamellar repeating distance (8.42-8.63 nm) and crystalline thickness (4.60-4.72 nm) were not different among stages indicating a complete lamellar structure even at early stage. The relative crystallinity was higher in dough (39.62 %) than milky (36.69 %) and mature starch (35.22 %) caused by molecular structure, amylose, and amylose-lipid complex. The short amylopectin branched chains (A and B1) in dough starch were easily entangled resulted in higher Payne effect and elastic dominant. Dough starch paste exhibited higher G'Max (738 Pa) than milky (685 Pa) and mature (645 Pa) starch. In a non-linear viscoelastic regime, small strain hardening was found in milky and dough starch. Mature starch showed the highest plasticity and shear thinning at high-shear strains as the long-branched chains (B3) microstructure was disrupted, disentangled, followed by chain orientation along shear.

Elevation of gamma-aminobutyric acid (GABA) and essential amino acids in vacuum impregnation mediated germinated rice traced by MALDI imaging.

Rice is known to contain limiting amino acids. Synthesis of GABA in plants is an adaptive response by initiating glutamic acid. A higher rate of GABA production was observed in samples enriched with glutamic acid and vacuum impregnation (VI) with longer germination time. Heat map profiles classified GABA and essential amino acids into 1) small increments consisting of Arg, His and Met, 2) moderate increments consisting of GABA, Trp, Lys, Phe and Thr, and 3) large increments consisting of Ile, Leu and Val. In Jasmine rice, highest essential amino acids were found in samples soaked with water, enriched with glutamic acid, and germinated for 72-96 h. Highest GABA (44.8 mg/100 g) was noticed after VI for 20-40 min and germinated for 72-96 h. In Riceberry, highest GABA (74.2 mg/100 g) and essential amino acids were associated with samples treated with VI for 20-40 min and germinated for 96 h.

Inhibitory effect of polysaccharides on acrylamide formation in chemical and food model systems.

The inhibitory effect of three polysaccharides (alginate, pectin and chitosan) on acrylamide formation was investigated in chemical and fried potato food model systems, under two heating regimes (heating block and microwave). In the chemical system, acrylamide formation followed a second order reaction kinetic behaviour. Activation energies (Ea) were 17.85 and 110.78 kJ/mol for conventional and microwave heating respectively. Acrylamide content was highest at 180 °C after 60 min conventional heating (27.88 ng/ml) and 3.5 fold higher after microwave heating for 60 s (800 W, 98.02 ng/ml). Alginate (0.3% w/v) and pectin (0.2% w/v) solutions efficiently inhibited acrylamide formation by 65% and 56% respectively under conventional heating, and 36% and 30% respectively under microwave heating. Coating potatoes with alginate, pectin and chitosan (1% w/v) prior to frying dramatically inhibited acrylamide formation by 54%, 51% and 41% respectively. However only alginate and pectin slightly reduced acrylamide by 5% in the microwave.

Retrogradation and Digestibility of Rice Starch Gels: The Joint Effect of Degree of Gelatinization and Storage.

Retrogradation affects acceptability of starchy foods; however, it is preferred in some products such as rice noodles. Amylose content, gelatinization temperature, and storage condition were reported to affect retrogradation but with disputed data. The joint effects of these parameters were interested in this study. Rice starch was gelatinized using different temperatures (77, 81, 95, and 121 °C) and stored isothermally with temperature cycles for 10 days. Results showed that the most important parameter that affected retrogradation was storage time followed by storage condition and gelatinization temperature. The recrystallization rate constant (k) and Avrami exponent (n) of retrograded starches stored under temperature cycle were higher than isothermal storage. All samples showed similar polymorphs of a mixture of B and V types. High-temperature gelatinized starch gel stored under temperature cycle condition produced higher yield of resistant starch. The study provided useful information on how to apply these parameters to control the retrogradation of starchy foods, especially rice noodle. PRACTICAL APPLICATION: Retrogradation is found to be more prominent at higher gelatinization temperature and longer storage time. Resistant starch produced from retrograded starch depended largely on storage time than storage condition. This finding can be applied to improve rice noodle qualities (by increasing retrogradation) with lower digestibility (by producing higher resistant starch).

Slow digestible colored rice flour as wall material for microencapsulation: Its impacts on gut bacterial population and metabolic activities.

Black waxy and red jasmine rice flour (6.5% and 18.7% amylose content, respectively) were modified using pullulanase followed by heat-moisture treatment (Hydrolyzed-HMT) to produce microcapsules that entrapped L. plantarum TISTR 1465. Hydrolyzed-HMT of colored rice flours showed restricted pasting properties, lower breakdown and higher thermal properties than native flour (p<0.05). Hydrolysis treatment was able to promote a low molecular weight starch that easily formed a crystalline structure after HMT. As a consequence, a significant increase in slowly digestible starch was observed (from 23.7% to 37.0% in waxy type and 22.2% to 34.6% non-waxy type). The survival of L. plantarum TISTR 1465 after simulated gastric fluid (90min) and simulated intestinal fluid (120min) of the Hydrolyzed 36h-HMT black waxy rice was higher (8.07±0.13logCFU/g and 7.48±0.12logCFU/g) than gum arabic (6.12±0.11 and 4.72±0.28logCFU/g) and no carrier (3.34±0.23 and 0.43±0.75logCFU/g) respectively. Moreover, these microcapsules also obtained the highest survival (8.67±0.20logCFU/g) after storage for 90days at 4°C. Under scanning electron microscopy, starch granules of the hydrolyzed 36h-HMT were seen as polyhedral shapes in the spherical aggregates that carried the microorganisms and reduced their injury and mortality. Short-chain fatty acids of the hydrolyzed 36h-HMT were much higher than positive control at every fermentation time (p<0.01). The fluorescence in situ hybridization result showed that the prebiotic property of hydrolyzed 36h-HMT black waxy rice can better aid the beneficial probiotic Lactobacillus spp. growth after 24h fermentation than the negative control (from 8.40±0.48 to 7.03±0.21logCFU/g, p<0.05) and commercial prebiotic Orafti®Synergy1 (8.40±0.48 to 7.47±0.08logCFU/g, p<0.01). Microencapsulation of hydrolyzed black waxy rice flour followed by HMT is proposed as a synbiotic ingredient to apply in synbiotic foods.

Effect of pretreatments and vacuum drying on instant dried pork process optimization.

Dehydrated meat which can be instantly rehydrated is needed by the industry. This research was aimed to investigate a more economical drying process. Central composite design was applied with three variables: cooking pressure, cooking time, and vacuum drying temperature. The responses were shear force (N), work of shear (N.mm) and % rehydration. The multiple linear regression equation models could predict 91.7, 90.9 and 94.8% of each response, respectively. Cooked pork meat was used for target responses. Its maximum shear force was 43.39±5.42 N, and work of shear was 419.50±64.17 N.mm. Vacuum drying temperature highly affected all responses. Validation of the predicted data was done using two optimum conditions. First condition was cooking pressure of 21.6 lb/in.(2), cooking time of 50 min, and vacuum drying temperature of 95°C. The second condition was cooking pressure of 38.4 lb/in.(2), cooking time of 35 min, and vacuum drying temperature of 100°C. A t-test confirmed that the observed data were not statistically different from the predicted data.