氮气气调储藏下不同温度对晚籼稻品质的影响

目的 探究氮气气调结合控温储藏对晚籼稻品质的影响。方法 本研究以广西桂林新收获的晚籼稻为对象,采用99%浓度的氮气包装,在高温(35℃)、常温(25℃)、低温(15℃)3个条件下的恒温培养箱中进行180 d的储藏。同时设立常规储藏条件作为对照,每30 d取一次样,进行加工、储藏品质及米饭蒸煮品质指标的测定。结果 在3个温度条件下,相比于常规储藏,氮气气调稻谷能够有效延缓出糙率和水分的下降。在35℃条件下,氮气气调稻谷的整精米率、品尝评分值下降幅度及黄粒米率、脂肪酸值、直链淀粉含量、米饭吸水率的上升幅度均较大。在15℃和25℃条件下,氮气气调稻谷则能够有效延缓整精米率和品尝评分值的下降,并抑制黄粒米率、脂肪酸值、直链淀粉含量和吸水率的上升。在25℃和35℃条件下,氮气气调能够抑制蒸煮后体积膨胀率的上升,但在15℃条件下的效果不明显。相关性分析显示,在种子储藏时应避免使用氮气气调。主成分分析结果表明,在25℃条件下,氮气气调比低温常规储藏效果更好,能够延缓稻谷品质劣变。而品质特征指标与储藏条件的相关性分析结果表明,储藏温度对稻谷品质的影响较小。结论 将温度控制在25℃的氮气气调储藏方式在经...     

不同贮藏温度下几种鱼的肉质品质变化对比

将草鱼、鳙鱼、鳜鱼、罗非鱼在不同温度下(4、-1和-20℃)贮藏0、3、6、9、12d,对4种鱼肌肉的水分、粗脂肪、pH值、肌纤维直径、质构特性、持水率、K值、总挥发性盐基氮(TVB-N)、TBARS进行测量。结果显示:相同贮藏温度下,其肉质品质随着贮藏时间的延长而变差,而贮藏的温度降低可以缓解该过程;另外肌肉的肉质特性与其贮藏间肉质品质变化有直接的关系,肌肉pH值越大、肌纤维直径越细、含水量和脂肪含量越低,在相同的贮藏温度和时间下,较其他鱼更能保持其肉质品质。     

Effects of germination time on phenolics,antioxidant capacity,in vitro phenolic bioaccessibility and starch digestibility in sorghum

The effects of germination time on phenolic, flavonoid, anthocyanin, antioxidant capacities, inhibition capacity of α-amylase, bioaccessibility of phenolic and digestibility of starch in sorghum were evaluated in this study. The levels of total phenolic, flavonoid and anthocyanin in germinated sorghum for 48 h increased by 39.74%, 37.28% and 52.21%, respectively. Germination also increased the composition of phenolic, flavonoid and anthocyanin in sorghum, and their antioxidant capacity and inhibitory rates of α-amylase. Additionally, in vitro digestion results showed that phenolic bioaccessibility increased by 10.18%, and digestibility of starch and expected glycaemic index (eGI) decreased by 13.87% and 5.26 in germinated sorghum for 48 h compared with the ungerminated sorghum. These results indicate that germination might be a green method to improve the nutritional quality of sorghum and promote the development of germinated whole-grain food.     

Delayed drying interval of red rice: Effects on cooking properties,in vitro starch digestibility and phenolics content

Maintaining the cooking characteristics and bioactive compound contents in red rice is essential during the post-harvest stages. For this reason, this study aimed to evaluate the influence of delayed drying time interval of 3 and 6 days and temperature of 15 and 25 °C followed by storage for 12 months on the cooking properties, in vitro starch digestibility, and the phenolic contents of red rice. The increased the delayed interval duration reduced the protein solubility, rehydration capacity, and free phenolic contents, and increased the cooking time and hardness after cooking in a temperature-independent manner. These changes reduced the starch digestibility of red rice. Increased the delayed interval duration also reduced the proanthocyanidin contents, consequently changing the grain color (decreased luminosity and increased a1 values). Thus, a delay in the interval duration before drying of 3 days at 15 °C showed the best results about the rice characteristics among the evaluated parameters; these conditions may be utilized when immediate drying is not possible.     

Kinetics of water diffusion in corn grain during the alkaline cooking at different temperatures and calcium hydroxide concentration

The kinetics of corn grains hydration during the nixtamalization process is described for different temperatures, cooking times and Ca(OH)₂ concentrations. Samples were prepared using different cooking times from 0 to 120 min; cooking temperatures of 62, 72, 82, and 92 °C, and Ca(OH)₂ concentrations of 0.0%, 0.8%, 1.0%, and 2.0% related to the mass of corn grains. The fitting of the experimental data to the empirical Michaelis-Menten equation gives a good approach of the hydration process. From the first derivate of the Michaelis-Menten equation the rate of the corn grain hydration can be obtained. This mathematical model predicts the hydration and hydration rate of the corn grains during the cooking time of the nixtamalization process. Furthermore, with this proposed model, we can predict that for short times the rate reaches its maximum, and tends to zero for long times as the saturation of the grain is reached. It is concluded that hydration and hydration rate of white corn grains depends significantly on the temperature and cooking water lime concentration (P < 0.005).     

Effects of different cooking methods on chemical compositions,in vitro starch digestibility and antioxidant activity of taro (Colocasia esculenta) corms

The impacts of different cooking methods (boiling, steaming, baking, microwaving and frying) on chemical compositions, starch digestibility and antioxidant activity of taro corms were investigated. Compared with raw taro, boiling and frying reduced crude protein and ash contents. Frying significantly increased crude fat and fibre contents but decreased carbohydrate content. All cooking methods reduced oxalate content, especially frying. Among the cooked products, the boiled taro had the highest rapidly digestible starch (RDS) but the lowest resistant starch (RS) contents. In contrast, the fried taro provided the lowest RDS but the highest RS contents. All cooking methods reduced the total phenolic content and antioxidant activity of taro. The boiled taro had the lowest antioxidant activity but the fired taro provided the highest. Frying was able to retain most of the health-promoting compounds with the lowest oxalate content; however, the high consumption of high-fat fried taro may adversely affect human health.     

Effect of irradiation,with and without cooking of maize and kidney bean flours,on porridge viscosity and in vitro starch digestibility

African traditional weaning foods are usually prepared from starchy flours at a total solids content of 50–100 g l^?1, giving a viscosity of 1000–3000 cP which is consumable by infants. These porridges have very low energy and nutrient densities. Processing to reduce the porridge viscosity and improve the energy and nutrient density may help in solving this problem. Maize, kidney bean and their 70:30 composite flours were irradiated at 0–10 kGy at room temperature. Irradiation greatly reduced the viscosity of porridges, probably by starch depolymerisation. Irradiation improved the starch digestibility of raw bean flours, possibly either by inhibiting α‐amylase inhibitors or by weakening the thick cell walls that enclose the starch granules, thus improving accessibility to enzymes. However, in raw maize, cooked maize and cooked bean flours there was maximum starch digestibility at a dose of 2.5 kGy, followed by small but significant decreases in starch digestibility at higher doses, more so in maize than in bean flours. The decrease in digestibility could be due to the formation of inhibitors of amylolytic enzymes (Maillard reactions products) or to the formation of resistant starch. Irradiation doses required to increase the total solids content of traditional maize‐ and/or bean‐based weaning porridges to at least 200 g l^?1 do not compromise starch digestibility significantly. © 2001 Society of Chemical Industry     

The impact of cooking method on the phenolic composition,total antioxidant activity and starch digestibility of rice (Oryza sativa L.)

This study investigated changes in the phenolic composition, total antioxidant activity (TAA) and starch digestibility in white and brown rice due to three different cooking procedures, and subsequent reheating of cooked rice after storage. Among the analyzed samples, brown rice showed the highest TAA and phenolic content (622.5 mg/kg DW). All cooking methods resulted in significant decrease of phenolic content and TAA of rice (p < 0.05). The greatest loss was observed after processing in rice cooker, which reduced phenolic content of both brown and polished rice by ～30% and ABTS radical‐scavenging activity by 20 and 28%, respectively. In general, the levels of polyphenols and TAA of cooked rice tended to further decline after storage and reheating, but to a much lesser extent when rice was prepared using microwaves. The application of in vitro digestion system disclosed that the microwave cooking resulted in the highest starch digestibility among cooking methods used.

Practical applications

Rice is one of the most commonly consumed staple foods worldwide. Scientific and epidemiological studies have showed that their phytochemicals exhibit antioxidant, anti‐inflammatory, antihypertensive and chemopreventive effects. Therefore, their high consumption, easy availability throughout the year and use as an additive to meat and high‐fat foods may make rice, especially in the form of whole grains, potentially important chemopreventive component of the diet. The appropriate cooking procedure of rice is crucial for preservation of bioactive compounds as well as digestion of starch and thus duration of the glycemic response. Preferably, this study is focused on the evaluation of the effect of cooking methods on the health‐related quality of rice. The results provide practical advice that the consumption of freshly cooked rice ensures its highest nutritional quality, while rice microwaving is recommended both when cooked rice will be reheated after storage (e.g., in restaurants) and accelerated starch digestion is in favor.     

发芽糙米在不同储存温度下品质变化的研究

采用模拟发芽糙米在打开包装的状态,通过比较发芽糙米水分、脂肪酸值、直链淀粉、γ-氨基丁酸、霉菌含量和细菌总数的变化,研究发芽糙米在5℃、常温(秋季)、35℃3种不同储存温度下品质的变化。结果表明:发芽糙米在存放过程中,温度对其水分、直链淀粉含量影响较小;但是对其γ-氨基丁酸、霉菌含量和细菌总数影响显著。发芽糙米在高温下储存,品质极易变坏,低温有利于发芽糙米的储存。     

High-amylose and Tongil type Korean rice varieties: physical properties,cooking behaviour and starch digestibility

Food Science and Biotechnology - The National Institute of Crop Science, Rural Development Administration (RDA) of Korea is presently developing new rice varieties suitable for producing Western...     

In vitro digestion rate and resistant starch content of tortillas stored at two different temperatures

In vitro indicators of starch bioavailability were evaluated in freshly prepared maize tortillas and compared to those exhibited by 24, 48 or 72 h-stored samples. Storage took place either at room temperature (approx. 25 °C) or under refrigeration (4 °C). Potentially available starch (AS) content decreased from 670 g kg⁻¹ in the control tortilla to 583 g kg⁻¹ in 72 h-stored preparations. Concomitant increases in total resistant starch (RS) and retrograded resistant starch (RRS) were recorded upon storage. RRS content in 72 h-stored samples (35-39 g kg⁻¹) doubled that of freshly prepared tortillas. Changes in AS, RS and RRS were not affected by storage temperature. Both initial rate and final point of starch hydrolysis by pancreatic amylase were reduced in samples kept for 48 and 72 h, without influence of storage temperature. Storage length is suggested as a major determinant of the bioavailability of starch in tortillas.     

贮藏温度对即食小龙虾品质及微生物菌群多样性的影响

先通过测定理化指标确定即食小龙虾货架期,再分别从4,25℃两种贮藏温度下中、末期的样品中提取即食小龙虾总DNA,通过高通量测序技术探究贮藏期间其微生物菌群变化。结果表明:随贮藏时间的延长,物种多样性逐渐降低;4℃贮藏条件下,末期优势菌群为海洋杆菌属(Oceanobacillus,81.522%)和希瓦氏菌属(Shewanella,3.625%);25℃贮藏条件下,末期优势菌群为哈撒韦氏菌属(Hathewaya,78.700%)、芽孢杆菌属(Bacillus,12.380%)和狭义梭菌属(Clostridium sensu stricto,8.707%)。     

Changes in proteins,physical stability and structure in directly heated UHT milk during storage at different temperatures

Changes occurring in directly heated UHT milk were studied during storage at 5, 22, 30 and 40 °C. Industrially produced UHT milk samples were analysed for changes in enzymatic activity, protein modification, destabilisation of casein micelles and relocation of milk proteins in relation to sedimentation and gel formation. Sedimentation occurred at all temperatures, and the protein composition of the sediments reflected the composition of its liquid phase; however, there was no α-lactalbumin, β-lactoglobulin or κ-casein present in sediments. Tendrils composed of β-lactoglobulin and κ-casein were seen on casein micelles after UHT treatment and grew in length prior to gelation. High degrees of lactosylation of proteins and peptides were clearly correlated with the absence of gelation and long tendrils. Gelled samples showed complete hydrolysis of intact β-casein, and limited lactosylation of β-lactoglobulin and κ-casein.     

Effects of cooking, drying and pretreatment methods on texture and starch digestibility of instant rice

Instant rice produced from a conventional process consisting of the cooking, washing and drying steps possesses poorer eating quality compared with that of freshly cooked rice. The objective of this work was therefore to study the effects of cooking, pretreatment and drying methods on microstructure, textural properties and starch digestability of instant rice after rehydration; jasmine white rice was chosen as a test material. Conventional boiling method and electric rice cooking were selected as the methods to prepare cooked rice. In the case of boiling, cooked rice was frozen at −20 °C or cooled at 4 °C for 24 h prior to drying, while the cooked rice from an electric rice cooker was washed with ambient or cool water for 30 s prior to drying. After pretreatment the cooked rice was dried either by freeze drying or hot air drying at 80 °C. Based on the scanning electron microscopic results it was found that the cooking, pretreatment and drying methods all affected the rice morphology. The hardness and stickiness of instant rice after rehydration were lower for samples prepared from the rice cooker than those of freshly cooked rice, while both textural properties appeared to be improved significantly for the samples from boiling. The texture of the freeze-dried products was not different from that of the air-dried one. The freezing pretreatment provided the texture and glycemic index of instant rice after rehydration similar to those of the freshly cooked rice. On the other hand, the cooling pretreatment resulted in the harder texture and higher glycemic index of the samples.     

Monitoring the sensorial and microbiological quality of pasteurized white asparagus at different storage temperatures

Changes in sensory quality and proliferation of pathogenic and spoilage microorganisms in pasteurized white asparagus were measured as a function of storage temperature. The main sensorial attributes studied with regard to storage time were the general appearance of the product, turgidity and package swelling. There was a significant correlation between the deterioration in sensorial quality and microbial evolution, which was even more marked at higher temperatures. After 13 days at 4°C, 6 days at 10°C, 5 days at 20°C and 84 h at 30°C organoleptic deterioration and, consequently, the end of shelf life were detected. A significant growth of spoilage flora was observed, which might be responsible for the drop in pH levels during the final period of analysis (from 6.3 to 3.5–4 until 148 h). There was greater lactic acid bacteria (LAB) growth as the temperature and CO₂ concentration increased, reaching a final concentration of approximately 10⁸ CFU g^?1 at all temperatures. We found no positive samples of Clostridium spp at 10 and 4°C. Among the species isolated at 20–30°C Clostridium septicum and in lower proportions Clostridium perfringens were encountered. The possible presence of Listeria monocytogenes was analyzed, but there were no positive samples in the final product. Pasteurized white asparagus maintains good organoleptic characteristics with a relatively long shelf‐life at low temperatures, which leads to an adequate acceptance among consumers. Copyright © 2006 Society of Chemical Industry