Effects Of Hydrothermal Treatments On Preparation Of Resistant Starch With Rice Powder

Resistant starch(RS)is a new and special source of functional dietary fiber.RS is now considered to provide functional properties and is now being utilized a variety foods products.Interest in research on resistant starch has considerably increased in China and internationally.In this study,rice was used as a raw material source of resistant starch.The effects of autoclaving,heat-moisture treatment(HMT),annealing(ANN),recrystallization,combined hydrothermal treatments,lipid on RS formation and their properties were investigated.Rice powder was treated by autoclaving,Heat-moisture treatment(HMT),annealing,recrystallization under different processing conditions,so as to study the effects of hydrothermal treatments(solid concentration,temperature and processing time)and recrystallization(cooling temperature,cooling time and repeat times).The result indicated that RS starch level increased in all samples after different hydrothermal treatments.Sample treated by autoclaving had the highest RS level(12.70%),nearly 6 times the RS level of raw rice powder.RS formation was more efficient when lower rice concentrations of were used and processed for extended periods of time in autoclaved samples.The RS level initially decreased as temperature increased but later increased exponentially with time.For Heat-moisture treatment(HMT)samples treated for short periods of time and solid concentration of 80% had higher RS levels.Increased processing temperatures had similar effects on autoclaved and HMT treated samples.For the annealed samples,an initial rise in RS level occurred with: increase in both solid concentration and processing time which then dropped,Temperature increase favored increased RS formation for these samples.Recrystallization at about 25 oC,using longer periods of time,and higher number of cycles resulted in increased RS levels.The properties of hydrothermal treated rice powder samples and their resistant starch were investigated.The result showsthat: rice protein content barely changed during hydrothermal treatments.After autoclaving and HMT,the moisture level of rice powder fell from 14.58% to 3.56% and 0.03%,whereas minimal changes occurred after annealing.Lipid content decreased significantly after hydrothermal treatments,and this was highly correlated to the formation of RS(P=2.12E-4<0.05).Total starch content decreased from 85.58% to 75.86%?82.16%?80.49% after autoclaving,HMT and ANN treatments respectively,indicating the formation of starch–lipid complexes.After autoclaving,HMT and ANN,the size of rice powder increased from 50 ?m to 500 ?m,180 ?m,1000 ?m respectively.The size of RS purified from hydrothermal treated rice powder by enzymatic treatmentwas much smaller than that of rice powder.Autoclaved samples had neat crystal structures with smooth surfaces while HMT sampleshad specific shield structures and ANN powder had loose and larger starch pellets.Autoclaving caused transition of crystallization from A-to a special B-type aggregates with X-ray pattern peaks at 2?=12.9°and 19.8° that were attributed to the formationof starch–lipid complexes,unlike the HMT & ANN treated samples that remained A-type.Autoclaved and HMT treated samples showed no gelatinization,whereas ANN samples still gelatinized at around 80.5 ?.Solubility and swelling abilities of hydrothermal samples were all enhanced with increase in treatment temperatures.Autoclaved samples,however,had unique solubility and swelling properties that could be attributed to the influence of a rice grain structure.Increase in treatment times resulted in decreased transparency,with the autoclaved and HMT treated samples decreasing at much faster rates than ANN and raw rice powder.In studies to determine the effects of combined-hydrothermal treatments,when the RS alone was considered concentrations obtained were of the order autoclaving > ANN then autoclaving > autoclaving then ANN > autoclaving then HMT > HMT then autoclaving > raw rice powder.Tests of properties indicated that HMT or ANN could inhibit the formation of RS or even deform existing RS in autoclaved rice powder with HMT having a greater effect than ANN.Influence of degreasing,monoglycerides,oleic acid on autoclaving efficiency was investigated.The result shows a slight decrease in RS level in degreased-autoclaved rice powder.Samples degreased and then had exogenous fat added showed a significant drop in RS after autoclaving.A positive correlation was obtained between the lipid doseand decrease in RS level.At the same lipid dosage,it is observed that oleic acid lowered RS more effectively than monoglycerides.