Exploration and Improvement of Acid Hydrolysis Conditions for Inulin-Type Fructans Monosaccharide Composition Analysis: Monosaccharide Recovery and By-Product Identification.

Acid hydrolysis serves as the primary method for determining the monosaccharide composition of polysaccharides. However, inappropriate acid hydrolysis conditions may catalyze the breakdown of monosaccharides such as fructans (Fru), generating non-sugar by-products that affect the accuracy of monosaccharide composition analysis. In this study, we determined the monosaccharide recovery rate and non-sugar by-product formation of inulin-type fructan (ITF) and Fru under varied acid hydrolysis conditions using HPAEC-PAD and UPLC-Triple-TOF/MS, respectively. The results revealed significant variations in the recovery rate of Fru within ITF under different hydrolysis conditions, while glucose remained relatively stable. Optimal hydrolysis conditions for achieving a relatively high monosaccharide recovery rate for ITF entailed 80 °C, 2 h, and 1 M sulfuric acid. Furthermore, we validated the stability of Fru during acid hydrolysis. The results indicated that Fru experienced significant degradation with an increasing temperature and acid concentration, with a pronounced decrease observed when the temperature exceeds 100 °C or the H2SO4 concentration surpasses 2 M. Finally, three common by-products associated with Fru degradation, namely 5-hydroxymethyl-2-furaldehyde, 5-methyl-2-furaldehyde, and furfural, were identified in both Fru and ITF hydrolysis processes. These findings revealed that the degradation of Fru under acidic conditions was a vital factor leading to inaccuracies in determining the Fru content during ITF monosaccharide analysis.

Influence of Selenium Biofortification of Soybeans on Speciation and Transformation during Seed Germination and Sprouts Quality.

Selenium (Se) biofortification during seed germination is important not only to meet nutritional demands but also to prevent Se-deficiency-related diseases by producing Se-enriched foods. In this study, we evaluated effects of Se biofortification of soybeans on the Se concentration, speciation, and species transformation as well as nutrients and bioactive compounds in sprouts during germination. Soybean (Glycine max L.) seedlings were cultivated in the dark in an incubator with controlled temperature and water conditions and harvested at different time points after soaking in Se solutions (0, 5, 10, 20, 40, and 60 mg/L). Five Se species and main nutrients in the sprouts were determined. The total Se content increased by 87.3 times, and a large portion of inorganic Se was transformed into organic Se during 24 h of germination, with 89.3% of the total Se was bound to soybean protein. Methylselenocysteine (MeSeCys) and selenomethionine (SeMet) were the dominant Se species, MeSeCys decreased during the germination, but SeMet had opposite trend. Se biofortification increased contents of total polyphenol and isoflavonoid compounds and amino acids (both total and essential), especially in low-concentration Se treatment. In conclusion, Se-enriched soybean sprouts have promising potential for Se supplementation and as functional foods.

Selenium Biofortification of Soybean Sprouts: Effects of Selenium Enrichment on Proteins, Protein Structure, and Functional Properties.

Selenium (Se) biofortification during germination is an efficient method for producing Se-enriched soybean sprouts; however, few studies have investigated Se distribution in different germinated soybean proteins and its effects on protein fractions. Herein, we examined Se distribution and speciation in the dominant proteins 7S and 11S of raw soybean (RS), germinated soybean (GS), and germinated soybean with Se biofortification (GS-Se). The effects of germination and Se treatment on protein structure, functional properties, and antioxidant capacity were also determined. The Se concentration in GS-Se was 79.8-fold higher than that in GS. Selenomethionine and methylselenocysteine were the dominant Se species in GS-Se, accounting for 41.5-80.5 and 19.5-21.2% of the total Se with different concentrations of Se treatment, respectively. Se treatment had no significant effects on amino acids but decreased methionine in 11S. In addition, the α-helix contents decreased as the Se concentration increased; the other structures showed no significant changes. The Se treatment also had no significant effects on the water and oil-holding capacities in protein but increased the foaming capacity and emulsion activity index (EAI) of 7S, but only the EAI of 11S. The Se treatment also significantly increased the antioxidant capacity in 7S but not in 11S. This study indicates that the dominant proteins 7S and 11S have different Se enrichment abilities, and the protein structures, functional properties, and antioxidant capacity of GS can be altered by Se biofortification.

Structural and physicochemical property changes during pyroconversion of native maize starch.

Pyrodextrins are widely applied in industry as adhesives, coatings, binders, and in food as dietary fiber. In this study, the dynamic changes of structure and physicochemical property during pyroconversion of native maize starch are investigated. By quantifying the variations of chain-length distribution (CLD) between native starch and pyrodextrins, it is found that 1) the long starch chains with degree of polymerization (DP) about 500-20000 are degraded while its content is not significantly varied between pyrodextrins; 2) the content of intermediate-long chains with DP 20-500 increases with temperature, indicating more pyrodextrin molecules with the equivalent Rh∼1.5-9.4 nm are newly formed; 3) the content of A and B1 chains are not largely varied between pyrodextrins with temperature ≤190 °C, suggesting that the repolymerization might be more likely occur in the amorphous lamellae. This study improves the understanding of structural and physicochemical property changes during the pyroconversion process of native maize starch.

Effect of dry heating treatment on multi-levels of structure and physicochemical properties of maize starch: A thermodynamic study.

Dry heating treatment (DHT) is a common process widely used in food industry. In this study, the thermodynamic effects of DHT on starch structure and physicochemical properties are investigated. The results show that, with heating temperature increasing during DHT, the molecular size, long-amylose chains with degree of polymerization (DP) ~5000-20,000, and the crystallinity of maize starch are significantly reduced while the granular structure is retained with slightly aggregation between starch particles. The solubility of DHT starch increases from 0.5% to 2%, indicating the majority of DHT starch is still insoluble. DHT affects starch thermal property greatly that, it decreases the gelatinization enthalpy while increases the heterogeneity of starch crystallites. With heating temperature increasing, DHT reduces the overall viscosity of starch paste. The rheological property of DHT starch is frequency-dependent, showing the typical shear thinning behavior and "solid-like" gel property. Especially, as heating temperature reaches 190 °C, the shear resistance becomes stronger, and it is closer to Newtonian fluid. The results prove the thermodynamic effects of DHT on multi-levels of starch structure and physicochemical properties, also indicating the great potential to utilize DHT in modifying starch properties and amplifying its applications.

The increased stickiness of non-glutinous rice by alkali soaking and its molecular causes.

Non-glutinous rice is always less sticky than glutinous rice. By soaking two non-glutinous rice (Jingmi and Xianmi) with different concentrations of NaOH solution, the stickiness of cooked non-glutinous rice is significantly increased, which is closely associated with the removal of surface proteins of these treated rice grains. By investigating starch leaching characteristics and the molecular structure of leached starch, we find: (i) total solids and amylopectin amount in the leached materials increase by raising NaOH concentration; (ii) the molecular size and chain-length distributions (CLDs) of leached starch significantly differ between samples with different soaking treatments; (iii) a strong correlation between stickiness of cooked rice and total amount of leached amylopectin is established. (iv) molecular causes for the increased stickiness of alkali-soaked rice are put forward to explain the above observations. This study could broaden the applications of non-glutinous rice by altering its stickiness attribute with alkali soaking.

Molecular causes for the increased stickiness of cooked non-glutinous rice by enzymatic hydrolysis of the grain surface protein.

Non-glutinous rice has higher amylose content but less sticky texture than glutinous rice. In this study, by soaking two non-glutinous rice with protease solution, rice stickiness is significantly increased and equivalent to that of glutinous rice. By exploring starch leaching behavior during rice cooking, we find: (i) total solids and amylopectin amount in the leachate are significantly increased by raising the protease concentration during the soaking treatment; (ii) molecular size and chain-length distribution (CLD) of leached starch from these protease-treated rice (PTR) significantly differed from the corresponding native starch; (iii) strong correlations between rice stickiness, amylopectin amount and the proportion of short amylopectin chains with degree of polymerization (DP) <36 in the leachate are established. The possible molecular mechanism for the increased stickiness of treated non-glutinous rice is put forward to explain the above result. This study could broaden the applications of non-glutinous rice for rice industry.

The importance of amylopectin molecular size in determining the viscoelasticity of rice starch gels.

Amylose content as the key indicator in determining the viscoelasticity of starch gels has been widely accepted. In this study, 7 rice varieties are deliberately selected to investigate the structural basis of gel viscoelasticity of starches with similar amylose content. By quantifying starch molecular structure and rheological properties of starch gels, we find (i) starch with similar amylose content forms significantly different gel networks in terms of K*, n* and tan δ; (ii) molecular sizes of rice starches are significantly different between samples; (iii) the chain-length distributions (CLDs) of both amylopectin and amylose are parameterized by mathematic model fitting, and no large variations of these fitted parameters between samples are observed; (iv) amylopectin size are negatively correlated with K* (p < 0.01) while positively correlated with tan δ (p < 0.05). Molecular mechanisms are put forward to explain the role of amylopectin size in contributing to the strength of gel network.

Molecular causes for the effect of cooking methods on rice stickiness: A mechanism explanation from the view of starch leaching.

Microwave, electronic pressure cooking (EPC), and water absorption method are the common but different ways used for cooking rice. To explore mechanisms for effects of cooking methods on rice stickiness, starch leaching behaviour and the fine structure of leached starch are investigated. We find: (i) EPC improves starch leaching, i.e. the highest amount for total solids and leached amylopectin (AP), while microwave restricts starch leaching; (ii) the chain-length distributions (CLDs) of leached AP between rice samples are similar while CLDs of leached amylose (AM) are mainly ranged between degree of polymerization (DP) 100 and 1000; (iii) microwave makes rice leaching more long-AM chains with DP 1000-10,000; (iv) the varied stickiness of differently cooked rice are mainly caused by total amount of leached materials, especially leached AP, rather than the molecular structure of leached starch. This mechanism explanation provides better view towards helping consumers improve cooking and eating quality of cooked rice.