Regulation Of The Physicochemical And Quality Characteristics Of Wholegrain Brown Rice By Applying High Hydrostatic Pressure Technology

As a wholegrain food,brown rice（WBR,Oryza sativa L.）shows the capability to substitute polished white rice（PWR）which tends to induce insulin resistance when as a major energy source.WBR includes pericarp,seed coat and intact germ where many physiologically important components exist,such as gamma-aminobutyric acid（GABA）,phenolic acids,flavonoid,gamma-oryzanol,minerals,dietary fiber and several vitamins.Correspondingly,the consumption of BR is linked to antihyperlipidemia,antihypertension and the reduction of cardiovascular diseases,obesity and cancer.Nevertheless,the widespread consumption of BR products is still limited by undesirable cooking properties,poor palatability and the presence of anti-nutritional factors（tannin,phytate,etc.）,as well as the rancidity triggered by lipase oxidation,particularly the relationship between sensory characteristics and nutrients distribution.Resultantly,the economic and scial values of consuming WBR as a staple are restricted.Although traditional thermal processing,such as emerging ultra-high temperature parboiling and extrusion treatment,is effective in improving textural properties and storability of WBR,bioactive components including phenolics,vitamins and GABA can be compromised.Therefore,considering that high hydrostatic pressure（HHP）,as an emerging nonthermal technology,shows great potential to improve cooking and texture attributes of the grains,this investigation explored the applicability of HHP technology by determining process-induced physicochemical changes and related mechanisms behind,using methods like processomics.Based on the results obtained,a processing strategy was proposed to simultaneously enhance WBR quality and nutritional attributes.Main results are summarized as follows:（1）The effects of germination and HHP processing on the in vitro bioaccessibility of mineral elements,amino acids（AAs）,antioxidants and starch in brown rice（BR）were investigated,based on an in vitro digestion model.Germinated BR（GBR）was obtained by incubating at 37^oC for 36 hour and then subjected to HHP treatments at 0.1,100,300 and 500 MPa for 10 min.Proximate analysis showed that free fatty acids（FFA）and moisture in GBR greatly increased after HHP treatment.The in vitro bioaccessibility of calcium and copper was increased by 12.59-52.17%and 2.87-23.06%after HHP,respectively,but bioaccessible iron was decreased（p<0.05）.In addition,HHP significantly improved individual AAs,particularly indispensable AAs and gama-aminobutyric acid,as well as bioaccessible total antioxidant activities and starch resistance to enzymatic hydrolysis.However,germination greatly increased starch digestibility.（2）The potential relationship between the micronutrients in vitro bioaccessibility and structural changes induced by HHP,as exemplified by representative minerals.HHP treatments were applied at 100,300 and 500 MPa for 10 min,and 0.1 MPa as control.Three representative minerals with different levels were chosen to assess the bioaccessibility,including phosphorus（P）,magnesium（Mg）and manganese（Mn）.The results demonstrated that the minerals bioaccessibility,measured by percentage solubility,were the highest when at 300 MPa whereas it decreased at 500 MPa.Correspondingly,microstructure imaging by scanning electron microscope（SEM）showed that the gelatinization of starch granule occurred at 300 MPa and it became more obvious when increased to 500 MPa.Atomic force microscopy characterization also suggested similar change in bran structure.With textural features to characterize structure changes,multivariate analysis by principal component analysis and canonical correspondence analysis indicated a negative correlation between the bioaccessibility and HHP-induced starch gelatinization.（3）GBR grains were obtained by incubating at 37 ^oC for 36 h,and subsequently subjected to HHP treatments at pressures 100,300 and 500 MPa for 15 min,using 0.1MPa as control.Headspace solid-phase micro extraction coupled to gas chromatography mass spectrometry was used to characterize process-induced shifts of volatile organic compounds fingerprinting.Quantitative results confirmed the significant reduction of total volatile fractions derived from germination process.Contrarily,the following HHP treatments greatly enhanced the flavor components of GBR,particularly characteristic odorants including aldehydes,ketones,and alcohols,indicating the potential application of HHP in enhancing flavor characteristics of GBR.Partial least square-discrimination analysis suggested that 4-vinylguaiacol was closely linked to germination,whereas E,E-2,4-decadienal,E-2-hexenal,E,E-2,4-heptadienal and benzyl alcohol could be volatile biomarkers of high pressure,implying possible induction of lipid oxidation by high pressure treatments.（4）The effects of HHP treatments（0.1-450 MPa/10 min）on chemical composition,microstructure,and the changes in chemical reactions during storage（20 days/30 ^oC）as indicated by volatile profiling,color development,and antioxidant activities for WBR grains,compared to high-intensity ultrasound（HIU）and germination（GER）pretreatments.Results showed that significant variation in physicochemical properties was caused by both processing approaches and storage duration.Color changes（a*,b*,L*,andΔE）were slightly noticeable after storage for all WBR samples,and HHP-treated grains represented clearly visible browning reactions.In addition,hierarchically clustered heatmap suggested that volatile fingerprinting could be preliminarily separated according to different pretreatments and storage duration.After immediate treatments,total antioxidant activities presented a decrease by 14-28%for all treated grains compared to the unprocessed samples.Within storage process,GER and HIU samples showed steadily declining trends for antioxidant activities whereas a fluctuation was observed in HHP-treated grains.Besides,samples treated by 350/450MPa maintained more antioxidants（91-102%）than the control（83-87%）,GER（64-76%）and HIU（76-88%）samples at the end of storage.Multivariate analysis revealed a close relationship between color changes and antioxidant activity.These results indicated the necessity of a complete evaluation for possible processing effects on physicochemical and nutritional characteristics of WBR grains within the entire process extending immediate treatments to its prolonged storage and consumption,for achieving better quality control using the optimized processing parameters.（5）The development of lipid hydrolysis and oxidation in WBR processed by emerging texture-improved techniques including high hydrostatic pressure（HHP;150-450 MPa/10 min）,high-intensity ultrasonication(HIU;17.83 w.cm^-2/30 min)and germination（37 ^oC/36 h）pretreatments during storage were investigated,in an attempt to ascertain a possible link between lipid degradation and the underlying mechanisms.The results showed that HHP and HIU treatments enhanced lipid hydrolysis and oxidation as indicated by the formation of free fatty acids（FFA）and thiobarbituric acid reactive substances（TBARS）respectively,whereas an opposite pattern was observed for germination.Storage process rather than after immediate treatments observed an increase in lipid oxidation of HHP and HIU-processed samples,which was related to processing-induced liberation of minerals.Quantitative and qualitative characterization via inductively coupled plasma-optical emission spectrometry（ICP-OES）and micro X-ray fluorescence（μ-XRF）analysis confirmed the shifts of mineral distribution in WBR grains in response to different pretreatments.The WBR-derived lipase was activated by Ca²⁺,andμ-XRF mapping indicated calcium enrichment in pericarp/aleurone layer and its mobilization to embryo during germination process where magnesium and manganese were significantly reduced.Multivariate analysis revealed a close relationship between increased lipid degradation and minerals including magnesium and manganese.（6）A novel processing pattern,combining HHP treatments with germination process,was proposed to enhance functionality and quality attributes of WBR,with the embryo growth and physicochemical characteristics explored.The grains were firstly subjected to mild HHP stress（30-90 MPa/5 min）and then incubated at 37 ^oC for 52 h for obtaining germinated samples（GBR）.The results showed that HHP shock resulted in a delayed embryo growth of WBR grains,maintaining acceptable sprouting rates ranging from 65%to 76%when germination was finished.The contents of gama-aminobutyric acid in GBR were greatly increased responding to HHP stress,showing pressure intensities dependent.Total digestible and resistant starch contents in samples stressed at 60/90 MPa were decreased,mainly associated with high pressure-induced amorphization as revealed by SEM imaging and FTIR,which promoted starch hydrolysis during germination.Besides,the levels of zinc and iron were influenced by HHP pretreatments due to the high pressure-mediated degradation behavior for phytic acids.The storability of HHP-stressed GBR grains was significantly enhanced through reducing free fatty acids formation and maintaining color stability during a storage testing.According to the results of MS-based metabonomics,multiple metabolic pathways,including saccharometabolism and phytic degradation,as well as the transformation of free and rejugated phenolic acids,were modified by HHP stress before germination.The current work demonstrated that mild HHP stress pretreatment prior to germination process could be used as a promising strategy to modulate certain physicochemical characteristics of WBR products.