Dietary Fiber From Defatted Rice Bran And Its Application To Bologna Sausage

Defatted rice bran (DRB), a byproduct of rice milling and rice bran oil extraction, is a good source of dietary fiber. Dietary fiber is the edible portion of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. It includes polysaccharides, oligosaccharides and associated plant substances and promotes beneficial physiological effects.Optimization of defatted rice bran total dietary fiber (TDF), insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) extraction (yield and purity) was studied using response surface methodology (RSM). The three-level four-factor Box-Behnken design was used to establish the optimum conditions for extraction yield and purity of TDF, IDF and SDF from DRB. The results showed:The highest yield of TDF (31.11%) was reached under condition0.15mol/L, NaOH concentration;60min, soaking time;150U/g a-amylase enzyme concentration and0.11AU/g, alcalase enzyme concentration with R2=0.9997The high purity of TDF (81.84%) was obtained under condition0.25mol/L, NaOH concentration;30min, soaking time;150U/g, a-amylase enzyme concentration, and0.10AU/g, alcalase enzyme concentration with R2=0.9838.The maximum yield of IDF (26.88%) obtained under condition0.20mol/L, NaOH concentration;30min, soaking time;180U/g, α-amylase enzyme concentration and0.10AU/g, a-amylase enzyme concentration with R2=0.9601while, the purity was90%with R2=0.9995under similar condition as TDF.The highest yield of SDF (2.69%) was obtained under condition0.25mol/L, NaOH concentration;60min, soaking time;180U/g, a-amylase enzyme concentration and0.10AU/g, alcalase enzyme concentration with R2=0.9762. The highest purity (53.57%) was reached under0.2mol/L, NaOH concentration;90min, soaking time;120U/g a-amylase enzyme concentration and0.10AU/g, alcalase enzyme concentration with R2=0.9068.The overall optimal conditions:0.15mol/L, NaOH concentration;64.03min, soaking time;137U/g and0.09AU/g,α-amylase and alcalase enzyme concentration, respectively and the optimal responses were TDF-yield=31.50±0.26%TDF-purity=79.71±0.22%; IDF-yield=27.44±0.43%IDF-purity86.77±0.05%; SDF-yield=2.35±0.06%and SDF-purity=51.57±2.11%.The DRB was subjected to high pressure (300,400and500MPa) for different times5,10and15min; and autoclaving at122and136℃for1h and extruded with screw speed at100and140rpm.It was found that IDF content significantly (p<0.05) increased when pressure increased from300to400MPa (28.62to32.09%at10min), while the increase in time affected moderately its content. However, autoclaving (122℃) and extruded (100rpm) bran showed significant (p<0.05) high soluble content (2.87and3.3%respectively). The observed redistribution of soluble sugars to insoluble ones under high pressure and insoluble sugars to soluble ones occurring autoclaving and extrusion might be explained these changes on DRB fiber contents.Physical properties, hydration properties, functional and physiological properties as well as antioxidant capacity of TDF, IDF and SDF were evaluated. The physical properties (density and porosity) except fat binding capacity of SDF were significantly higher than that of IDF and TDF (bulk density:1005.81mg/ml vs.395.47mg/ml and porosity:1.932cm3/g vs.0.429cm/g respectively).The hydration properties of SDF was lower than that of IDF and TDF (water holding capacity:3.27g/g vs.2.11g/g; water binding capacity:4.16g/g vs.1.29g/g and swelling capacity:1.39ml/g vs.0.65ml/g for IDF and SDF respectively; p<0.05).Compared to SDF, IDF showed the highest CEC, while its GDRI value was the lowest7.49%at30min (p<0.05). SDF significantly lowered concentration of cholesterol, and was better than IDF (29.90%vs.7.5%respectively at pH7); however the adsorption capacity of bile salt of IDF was higher than that of SDF (18.20%vs.13.76%; p<0.05). All dietary fibre fractions at high concentration (5%or50mg/ml) showed a high antioxidant activity.Dietary fiber isolated from DRB was treated by micronization, ultrasound, microwave and extrusion cooking to get physically modified fibers. In-vitro studies of functional properties of these fibers under gastrointestinal conditions (temperature, pH and transit time) showed that all fibres had significantly (p<0.05) high hydration capacity in pH8.7with the highest values of WBC and SWC for extruded fibres (4.68g/g and3.66ml/g respectively), while CEC was lower in pH1.8(0.15meq/g for micronization treated fibre, the lowest). Extruded fibre showed higher GDRI (40.73%), thus higher glucose adsorption capacity (4161μmol/g) and exhibited maximum retarding effect on the flow of glucose across the dialysis bag for9h compared to other treatments.In-vitro fermentation by human fecal bacteria of modified fibers showed the major fermentation products were propionic, acetate and butyrate acid. Fermentation of extruded fiber gave the highest amounts of propionic and acetic acid135.76and25.45mmol/L respectively, while, the fermented product with microwaved fiber had the highest butyric acid content (10.75mmol/L). The amount of short-chain fatty acid increased from12h to24h and propionic acid was the predominant.The study of in-vitro bile salts binding showed that extruded fiber had higher affinity with sodium deoxycholate and sodium chenodeoxycholate (66.14and30.25%) while microwaved fiber exhibited the highest affinity with sodium taurocholate (14.38%).Incorporation of defatted rice bran fibers (untreated and treated) to sausage caused a deterioration of texture and sensory qualities however; bologna with5%added of all treated fibers and10%added of micronized fiber fibers exhibited acceptable sensory and textural qualities.Therefore, these physically modified fibres showed important improved functional and physiological effects (hypoglycemic, hypocholesteromic effects) and can be incorporated as low calorie bulk ingredient in foods to reduce calorie level.