| Compared with white rice(WR),brown rice(BR)has more comprehensive nutrition and higher utilization rate.Eating BR instead of WR is beneficial to health and saves food.However,there are three drawbacks of BR.Firstly,the hard and rough texture,poor digestibility and tendency to lipid rancidity limits consumer acceptance.In this research,high pressure(HP),freeze-thaw cycles(FTC)and germination-parboiling(GP)treatments were used to improve the edible quality of BR.For HP treatment,BR was treated at 200 MPa for 10 min and 5+5 min,marked as HP-10 min and HP-5+5min respectively.For FTC treatment,BR was frozen at-20 °C for 1 h and then immediately thawed at 35 °C for 40 min,and the treatments were repeated for 2cycles FTC(FTC-2)or 4 cycles FTC(FTC-4).For GP treatment,BR was germinated for 12 h or24 h(marked as G12 P and G24P),followed by parboiling for 10 min with steam.Taking untreated BR and WR as the control group,the texture and color,the digestibility of starch,protein,fat,and rancidity during storage of treated BR were compared and analyzed.The mechanism of different treatements on BR was researched by analyzing the phychemical properties.The main results are as follows:1.Only GP treatment reduced the L* value of BR.As for textrure,FTC showed the best effect in reducing the hardness of BR(38-41%),and FTC treated BR was the closest to WR in texture.Improved water absorption ratio,HP and FTC induced modification of rice bran layer and GP induced partial starch gelatinization were considered to be responsible for improving texture of BR.2.By comparing starch digestibility,BR treated with FTC had higher resistant starch content and lower glycemic index(GI)value.The starch digestibility of BR treated with GP was the best and closest to that of WR.BR treated with HP and GP can be defined as a high GI food.3.BR-AAS was designed to evaluate the nutritive value of free amino acids released after digestion(on the premise of same intake of BR products),and the results indicated that G24 P was the best choice for human to supplement intake of amino acids.The degree of starch digestion would affect the digestibility of protein.HP,FTC,GP treatment decreased the protein solubility of BR protein,due to the change of surface hydrophobicity.Besides,all treatments increased the disulfide bonds content of BR protein,meaning more stable structure of protein.4.GP treated BR released more palmitic acid,stearic acid,oleic acid and linoleic acid than untreated BR after digestion.FTC and HP treatments increased the release of palmitic acid and stearic acid,while opposite results were observed in oleic acid and linoleic acid.According to the digestibility of BR fat,G12 P should be the best choice.5.HP and GP inhibited the lipid rancidity of BR during storage.FTC treated BR showed higher fatty acidity and conjugated dienes contents during storage(up to 69 mg KOH/100 g and115 μmol/100 g,respectively),while malonaldehyde content was stable,which may be due to the balance between oxidation production and rapid volatilization. |
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