Microstructural and physicochemical properties of heat-moisture treated waxy and normal starches

Starches from normal rice (21.72% amylose), waxy rice (1.64% amylose), normal corn (25.19% amylose), waxy corn (2.06% amylose), normal potato (28.97% amylose) and waxy potato (3.92% amylose) were heat-treated at 100 °C for 16 h at a moisture content of 25%. The effect of heat-moisture treatment (HMT) on morphology, structure, and physicochemical properties of those starches was investigated. The HMT did not change the size, shape, and surface characteristics of corn and potato starch granules, while surface change/partial gelatinization was found on the granules of rice starches. The X-ray diffraction pattern of normal and waxy potato starches was shifted from B- to C-type by HMT. The crystallinity of the starch samples, except waxy potato starch decreased on HMT. The viscosity profiles changed significantly with HMT. The treated starches, except the waxy potato starch, had higher pasting temperature and lower viscosity. The differences in viscosity values before and after HMT were more pronounced in normal starches than in waxy starches, whereas changes in the pasting temperature showed the reverse (waxy > normal). Shifts of the gelatinization temperature to higher values and gelatinization enthalpy to lower values as well as biphasic endotherms were found in treated starches. HMT increased enzyme digestibility of treated starches (except waxy corn starch); i.e., rapidly and slowly digestible starches increased, but resistant starch decreased. Although there was no absolute consistency on the data obtained from the three pairs of waxy and normal starches, in most cases the effects of HMT on normal starches were more pronounced than the corresponding waxy starches.     

Effects of microwave heat-moisture treatment on properties of waxy and non-waxy rice starches

Waxy and non-waxy rice starches adjusted to 20% moisture (wet basis, w.b.) were heat-moisture treated in a microwave oven to determine the effects of the microwave heating characteristics on digestibility, pasting, and morphological properties of the heated starches. Microwave heating produced only minimal changes in digestibility as well as the physical characteristics of heated starches. Significant changes in viscosity properties after microwave heat treatment were observed for both waxy and non-waxy starches heat-treated in a microwave oven, relative to non-treated samples. Non-waxy starch heated in microwave oven showed an increase in breakdown viscosity from 29.8 RVU (non-treated starch) to 35.8 RVU after heating for 60 min. However, for waxy starch, breakdown viscosity decreased from 112.7 to 35.9 RVU after 60 min of microwave heat treatment, reflecting an increased stability of microwave heat-treated starch under cooking. The data obtained in this study indicate that there was much higher re-aggregation of starch granules in waxy starch after microwave heat treatment than occurred in non-waxy starch, suggesting a re-association of amylopectin branch chains in the heat-treated waxy starch.     

Slowly digestible starch from heat-moisture treated waxy potato starch: Preparation,structural characteristics,and glucose response in mice

Heat-moisture treatment (HMT) was optimised to increase the formation of slowly digestible starch (SDS) in waxy potato starch, and the structural and physiological properties of this starch were investigated. A maximum SDS content (41.8%) consistent with the expected value (40.1%) was obtained after 5 h 20 min at 120 °C with a 25.7% moisture level. Differential scanning calorimetry of HMT starches showed a broadened gelatinization temperature range and a shift in endothermal transition toward higher temperatures. After HMT, relative crystallinity decreased with increasing moisture level and X-ray diffraction patterns changed from B-type to a combination of B- and A-types. Hollow regions were found in the centres of HMT waxy potato starches. HMT intensity significantly influenced SDS level. This study showed that HMT-induced structural changes in waxy potato starch significantly affected its digestibility and the blood glucose levels of mice who consumed it.     

微波湿热处理对马铃薯抗性淀粉含量及性质的影响

在湿热条件下,采用不同微波条件对马铃薯淀粉进行处理,运用扫描电子显微镜、布拉本德粘度仪,对微波处理前后的物化性质进行了研究。结果表明,经微波辐射处理后,淀粉颗粒表面会出现小孔和凹坑;马铃薯淀粉中抗性淀粉和直链淀粉的含量、糊化转变温度及其范围、热糊稳定性和凝沉性得到提高;马铃薯淀粉的膨胀度、溶解度和粘度降低。      

酶法处理马铃薯渣对其功能性质的影响

以马铃薯渣中的膳食纤维组分为研究对象,研究了纤维素酶单一处理及耐高温α-淀粉酶结合纤维素酶复合处理马铃薯渣对其功能性质的影响。经过酶处理的马铃薯渣可溶性膳食纤维含量显著提高,单独使用纤维素酶水解马铃薯渣,可溶性膳食纤维（SDF）含量达14.38g/100g,比原浆提高了18.74%,采用耐高温α-淀粉酶结合纤维素酶复合处理的马铃薯渣中SDF含量达15.00g/100g,与单独使用纤维素酶水解相比提高了4.31%,与原浆相比提高了23.86%。扫描电镜分析发现薯渣经过酶解后,结构变得松散,处理后马铃薯渣的阳离子交换能力、膨胀率、持水力及持油力明显提高,且双酶组效果最好,与市面上的麸皮相比性能更优,薯渣中残余的淀粉更易消化,在饲料中有较好的应用潜力。      

Effect of acid treatment on the physicochemical and structural characteristics of starches from different botanical sources

Starch and starch derivatives (maltodextrins) are used as encapsulating materials. Starch for use as encapsulating material could be subjected to mild acid treatment. However, the granule size and organization of starch components (AM and AP) play an important role in the acid treatment. The aim of this research was to produce modified starch that might be used as encapsulate material, applying moderate acid‐treatment with 3 N sulphuric acid in a ratio 1:5 w/v for 3 h at 60°C, in starches from different granule size, evaluating their morphological, physicochemical, and structural features. Acid treatment has an effect in the AM content and the outcome was higher in starch with larger granule size. Bimodal granule size distribution was found in acid‐treated rice and maize starches. Erosion and exo‐corrosion were observed in acid‐treated starches with SEM. The XRD pattern did not change with the acid treatment, the native and acid‐treated samples showed similar crystallinity values, except rice starch. The branching degree was higher for modified potato starch, showing higher branching points, modified starches had shorter chains with increased A‐chains, and decreased B3+ chains, and the effect was higher in cereal starches; modified starches had a higher degree of retrogradation and they did not show pasting properties. The internal organization given by the granule size is an important parameter in the acid treatment of starches as it affected their physicochemical and structural features, and in the end, their functionality as encapsulate agent.     

Effect of acid hydrolysis in the presence of anhydrous alcohols on the structure,thermal and pasting properties of normal,waxy and high‐amylose maize starches

Maize starches with different amylose contents (0%, 23% and 55%) were treated in anhydrous methanol, ethanol, 2‐propanol, 1‐butanol with 0.36% HCl at 25 °C for 5 days. Results showed that the extent of change in physicochemical properties increased from methanol to butanol. Treated waxy maize starch showed higher than 65% solubility at above 75 °C. The diffraction peak at 2θ = 5.3° of amylomaize V starch disappeared after treatment in ethanol, 2‐propanol and 1‐butanol. Acid–alcohol treatment decreased the gelatinisation temperature of normal (from 64.5 to 61.9 °C) and waxy maize (from 68.1 to 61.1 °C) starches, while it increased that of amylomaize V (from 68.7 to 72.3 °C) starch. The extent of the decrease in the pasting viscosity followed the following order: amylomaize V < normal maize < waxy maize. This study indicated that acid–alcohol treatment degraded preferentially the amorphous regions and the different changes depended on the crystal structure and amylose content of starch.     

不同温度热处理对4种食用油氧化稳定性的影响

将油茶籽油、大豆油、菜籽油、食用植物调和油分别在不同温度（100~200 ℃）条件下加热2 h,测定酸值、过氧化值、共轭二烯值、共轭三烯值、硫代巴比妥酸（TBARS）值变化,研究4种食用油在不同温度下的氧化稳定性。结果表明：4种食用油的酸值、过氧化值、共轭二烯值、共轭三烯值、TBARS值均随加热温度的升高而升高,说明随着加热温度的升高,4种食用油的氧化程度均明显增加。与未加热油样对比,4种食用油各指标增量从大到小顺序分别为：酸值,油茶籽油>菜籽油>食用植物调和油>大豆油;过氧化值,食用植物调和油>油茶籽油>菜籽油>大豆油;共轭二烯值、共轭三烯值,菜籽油>大豆油>食用植物调和油>油茶籽油;TBARS值,食用植物调和油>菜籽油>大豆油>油茶籽油。同步荧光光谱分析表明,在高温下4种食用油自身所含有的酚类吸收峰（360~390 nm）下降或峰形变窄,表征氧化产物的峰（413~520 nm）升高（除调和油）,说明4种食用油在发生氧化的同时组分也发生了改变。     

Effect of pH at heat treatment on the hydrolysis of κ-casein and the gelation of skim milk by chymosin

Skim milk was adjusted to pH values between 6.5 and 7.1 and heated at 90 °C for times from 0 to 30 min. After heat treatment, the samples were re-adjusted to the natural pH (pH 6.67) and allowed to re-equilibrate. High levels of denatured whey proteins associated with the casein micelles during heating at pH 6.5 (about 70-80% of the total after 30 min of heating). This level decreased as the pH at heating was increased, so that about 30%, 20% and 10% of the denatured whey protein was associated with the casein micelles after 30 min of heating at pH 6.7, 6.9 and 7.1, respectively. Increasing levels of κ-casein were transferred to the serum as the pH at heating was increased. The loss of κ-casein and the formation of para-κ-casein with time as a consequence of the chymosin treatment of the milk samples were monitored by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The loss of κ-casein and the formation of para-κ-casein were similar for the unheated and heated samples, regardless of the pH at heating or the heat treatment applied. Monitoring the gelation properties with time for the chymosin-treated milk samples indicated that the heat treatment of the milk markedly increased the gelation time and decreased the firmness (G^′) of the gels formed, regardless of whether the denatured whey proteins were associated with the casein micelles or in the milk serum. There was no effect of pH at heat treatment. These results suggest that the heat treatment of milk has only a small effect on the primary stage of the chymosin reaction (enzymatic phase). However, heat treatment has a marked effect on the secondary stage of this reaction (aggregation phase), and the effect is similar regardless of whether the denatured whey proteins are associated with the casein micelles or in the milk serum as nonsedimentable aggregates.     

Effects of pepsin hydrolysis on the soy β‐conglycinin aggregates formed by heat treatment at different pH

The effects of pepsin hydrolysis on the β‐conglycinin aggregates formed by heat treatment at different pH were investigated. Results showed that fibrils were still observed, whereas the random aggregates were easily to be digested in the simulated gastric fluid. Electrophoresis and molecular weight analysis indicated that large aggregates still existed after pepsin treatment for fibrils. Hydrolysis resulted in changes in the apparent viscosity (ηapp) of 6% fibril solutions. The ηapp at the shear rate range (0–30 s^?1) increased in the order of fibrils < fibrils with pepsin for 60 min < fibrils with pepsin for 30 min. Smaller peptide/fibril fragments were generated, and additional aggregates were reformed during the hydrolysis process, as evidenced by thioflavin T and atomic force microscopy images. The native β‐conglycinin hydrolysates comprised a mixture of polypeptides enriched in about 47 kDa. These findings would provide valuable information about effects of enzymatic hydrolysis on plant oligometric globulin aggregates.