| Lipid in rice mainly distributes in the aleurone layer and embryo,and is removed when rice is milled during processing,thus cannot be utilized by the human body.Endosperm lipid in normal rice is usually lower than 1%,and the effects of this part of lipid on rice physicochemical and nutritional properties are always neglected.In past studies,our lab bred a series of rice mutants that derived from the same parent obtaining different endosperm lipid content(0.81-2.42%)by using gamma irradiation.However,from farm to table,rice needs to be stored and cooked,whether the high content of endosperm lipid would affect the storing and cooking properties of rice is still unknown.The effect of the starch-lipid complex on human intestinal digestion and fermentation is also unclear.This study compared the storage,cooking,digestion and fermentation properties of various rice mutants differential in endosperm lipid content,and the following are the main results:(1)An artificially accelerated rice ageing method was established,and aged samples of high lipid rice ALK3/RS4(lipid content 2.32%/2.36%)and low lipid rice GZ93(lipid content 0.81%)were quickly obtained.The fatty acids profile between high lipid rice and low lipid rice are very similar whether before or after ageing.After ageing,the total lipid content of all samples did not change,while the UFA : SFA of NSL and setback decreased,indicating the lower oil quality and rice eating and cooking quality.However,compared to the low lipid rice,high lipid rice exhibited no more serious quality deterioration after ageing.ALK3 had a high γ-oryzanol content(130.5 μg/g),which is significantly higher than that in GZ93(3.0 μg/g).Even after ageing,the γ-oryzanol content in ALK3 is 44 times higher than that in GZ93.These results suggested that the high endosperm lipid does not affect the storage property of rice,and instead contributed to a better nutritional quality.(2)According to the analysis of composition and static in vitro simulation of gastrointestinal food digestion(INFOGEST)of five rice varieties,the high lipid rice ALK3 and GZ1 had significantly higher resistant starch content(> 9.1%)and lower estimated glycemic index(< 70)than the low lipid rice.After a two-step lipid removal of the three chosen varieties(ALK3,RS4 and GZ93),the digestion rate of high lipid rice by α-amylase increased,and is similar to that digested by pancreatin(containing α-amylase and pancreatic lipase),but this phenomenon was not observed in the low lipid variety GZ93.After digestion,high lipid rice ALK3 and RS4 had a high bioaccessible γ-oryzanol content(80.6 and 7.9 μg/g,respectively),which is 47 and 5 times higher than that in GZ93.These results indicate that the endosperm lipid(mainly triglycerides),can transfer part of starch into a kind of “slowly digestible starch” by complexing with starch,thus lowering the glycemic index of rice and enhancing its nutritional quality.(3)The in vitro fermentation and 16 S rRNA sequence analysis of the microbiota showed that,compared to the rice flour/starch samples,the starch-lipid complexed sample can produce a higher content of short chain fatty acids(SCFAs)and a higher proportion of propionic acid after fermentation,as well as a lower α-diversity and a significantly different β-diversity,indicating the special fermentation properties of the resistant starch type five.The starch-lipid complexed sample of RS4 and GZ93 are of high similarity in phylum and genera classification and predicted gene function of the microbiota.Compared to the rice flour/starch samples,the starch-lipid complexed samples also had a higher abundance of Bacteroidetes and Proteobacteria,while a lower abundance of Firmicutes in phylum level,and a higher abundance of propionic acid-producing bacterium such as Bacteroides and Parabacteroides after fermentation.Compared to GZ93,RS4 produced more SCFAs and microbiota with different predicted gene functions after fermentation.(4)Three different household cooking methods(pre-soaked cooking,acidic cooking,alkalic cooking)were adopted,and parameters i.e.water uptake ratio,viscosity during gelatinization and texture property were measured to indicate the palatability of cooked rice.The digestion property of the cooked rice is also measured,and the low digestibility of RS4 was maintained under all cooking methods.After pre-soaked cooking,RS4 had a higher water uptake ratio,a higher proportion of leaked starch and a lower setback,the RS4 grains had higher cohesiveness while lower hardness and resilience.The results show that pre-soaked cooking could enhance the palatability of high lipid rice RS4 while maintaining its low digestibility,making it more acceptable to customers.The results suggested that high lipid rice had a relatively low glycemic index,high bioaccessible γ-oryzanol content,and the fermentation of starch-lipid complex(RS5)can specifically adjust the intestinal microbiota.In the meanwhile,the high endosperm lipid did not bring much effect on rice storage properties,and pre-soaked cooking as a household cooking method can enhance the palatability of high lipid rice while maintaining its low digestibility.High lipid rice has large potential in the industry and provides a new sight in breeding functional nutritional rice by modifying the endosperm lipid. |
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