莲子微波真空干燥特性及动力学模型的研究

为探究莲子微波真空干燥过程中水分变化规律,本文以新鲜莲子为对象,考察不同微波强度和真空度对莲子微波真空干燥特性的影响,在此基础上构建其干燥动力学模型。结果表明,莲子微波真空干燥过程为降速干燥阶段,微波强度和真空度对莲子干燥速率和干燥时间影响均显著(p<0.05)。随着微波强度和真空度的增大,莲子干燥速率增加,干燥时间缩短。经6种干燥模型非线性回归拟合发现,Tian模型R2最高,RMSE、SSE及χ2最小,该模型能较好地描述和预测莲子微波真空干燥过程中水分变化规律。      

Comparison of enzyme‐assisted and ultrasound‐assisted extraction of vitamin C and phenolic compounds from acerola (Malpighia emarginata DC.) fruit

This article describes a comparative study of enzyme and ultrasound techniques for the simultaneous extraction of vitamin C and phenolic compounds from acerola fruit. Ultrasound‐assisted extraction (UAE) took only 6 min to achieve the highest level of vitamin C and phenolic compounds as well as antioxidant activity of acerola juice, while enzyme‐assisted extraction (EAE) took up to 120 min to obtain the maximal values. On the basis of kinetic model of second‐order extraction, the extraction rate constant of vitamin C and phenolics in UAE increased approximately 3.1 and 2.7 times, respectively, in comparison with that in EAE. In addition, the maximal level of vitamin C, phenolics and the antioxidant activity evaluated by 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH), and 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) methods in UAE was 4.6%, 3.5%, 4.6% and 3.3%, respectively, higher than those in EAE. Obviously, UAE is a useful method for the extraction of antioxidants from plant materials.     

Shelf life of fresh‐cut green beans as affected by packaging systems

To reduce quality loss of fresh‐cut green beans, different packaging systems were studied. In particular, samples were packaged in micro‐perforated and no‐perforated films and stored at 5 °C; unpackaged fresh‐cut green beans were also stored at the same temperature as the control. Headspace gas concentrations, mass loss, sensory quality and microbial proliferation were monitored for about 3 weeks. Results confirmed that selection of proper packaging is of crucial importance to create conditions able to guarantee the maintenance of product quality. Shelf life of fresh‐cut green beans packaged in the no‐perforated film (polyethylene, 25 μm) and in two micro‐perforated films (polypropylene films with 7 and 4 micro‐holes per package) was higher (19.2, 18.13 and 17.7 days, respectively) than that of the control or samples packaged in the micro‐perforated film with 12 micro‐holes per package (16.5 days).     

Effects of cooking and drying on phenolic compounds and antioxidant activity of African green leafy vegetables

Phenolic compounds play a significant role in our diets due to their proposed health benefits in the human body. Their presence in plants has therefore led to the increase in recognition of underutilized African green leafy vegetables (ALVs) as vital contributors to the food supply, which in itself is a component of food security in Africa. However, most ALVs are cooked prior to consumption or dried for preservation purposes. Cooking and drying of ALVs may induce chemical and physical changes to ALVs, thus affecting their phenolic composition and resultant health promoting properties. This review, therefore, aims to elucidate the several effects exerted upon ALV’s phenolic composition and antioxidant activity as a result of cooking and drying as well as a brief discussion on the health benefits correlated with ALV consumption.     

Comparison of the effect of microwave freeze drying and microwave vacuum drying upon the process and quality characteristics of potato/banana re‐structured chips

This study investigated the drying characteristics of microwave freeze‐drying (MFD)/microwave vacuum drying (MVD) of banana/potato restructured chips of varying proportion and microwave power. The results showed the MFD drying time had a maximum one‐hour time difference between the samples treated with 2 W g^?1 and 3 W g^?1 microwave power; and the higher potato content samples have about 30 min predominance than low potato content samples in drying time and the total drying time of MVD samples was less than 60 min. For the rehydration ratio, MFD samples were far superior to the MVD samples. The MFD samples had more than 4.5 rehydration ratio. The data of the colour difference metre showed that 3 W g^?1 microwave power would make samples slightly charred. The biggest differences between the MFD and MVD chips lie in their texture and shape; the hardness of MVD samples was 30.86 N, thrice higher than MFD samples.     

Hot air drying of tea flowers: effect of experimental temperatures on drying kinetics,bioactive compounds and quality attributes

The drying process is important for the quality and value of tea flower products. In the present work, the effects of different hot air drying (HAD) temperatures from 60 to 120 °C on drying kinetics, bioactive compounds (catechins, flavonol glycosides and triterpenoid saponins) and quality attributes (volatile compounds, colours and antioxidant properties) of tea flowers were systematically evaluated. The results showed that higher drying temperature resulted in a shorter drying time but with greater loss of bioactive compounds and quality attributes. Flowers subjected to HAD at 60 °C showed the highest bioactive contents and quality attributes of all HAD samples and the quality of HAD 60 °C samples were close to that of freeze-dried samples. Taking account of the production efficiency and energy consumption, the tea flowers dried at 60 °C for 180 min was preferred. These findings provide a guide for the processing of tea flowers with the aim of improving the overall quality of the product.     

Physicochemical,rheological, and molecular characterization of colloidal gelatin produced from Common carp by‐products using microwave and ultrasound‐assisted extraction

The effects of ultrasound‐assisted extraction (UAE) and microwave‐assisted extraction (MAE) methods on molecular and physicochemical characteristics of the resultant gelatin were examined. Before extraction procedure, we investigated the optimum pH for swelling of Common carp by‐products, which is an important pretreatment for gelatin production. The highest swelling yield was achieved at pH 13 among pH 1–14 with unit intervals. Results indicated that the UAE gelatin has a higher gel strength, viscosity, melting point, and gelling point. The power and time of sonication showed a reverse relation with these characteristics. In addition, as the time of microwave heating was raised, the gel strength, viscosity, melting point, and gelling point were decreased. The FT‐IR spectra showed similar peaks but the Amide B in UAE gelatin slightly vanished. The electrophoretic pattern also revealed the higher gel strength and viscosity of UAE gelatin due to the higher intensity of α and β chains compared to MAE gelatin. It can be concluded from all of the results of this study that the produced gelatin using these procedures can be a good source of gelatin in food and drug industries.     

Degradation kinetics of total phenolic compounds,capsaicinoids and antioxidant activity in red pepper during hot air and infrared drying process

Degradation kinetics of total phenolic compounds, capsaicinoids and antioxidant activity in red pepper during both hot air drying and infrared drying were investigated, as well as the correlation between antioxidant compounds and antioxidant capacity was discussed in current study. The fractional conversion kinetic and first order kinetic models were proved to describe the changes of total phenolic compounds vs. drying time and moisture content, respectively. Degradation of capsaicinoids and antioxidant capacity vs. drying time and moisture content both followed fractional conversion kinetic model. Infrared drying accelerated the degradation rate of total phenolic compounds and capsaicinoids vs. drying time as compared with hot air drying at the same temperature; however, a contrary result was found that infrared drying decreased the degradation rate of both total phenolic compounds and capsaicinoids vs. moisture content. Total phenolic compounds exhibited a stronger relationship with antioxidant capacity of red pepper analysed by multiple linear regression analysis.     

Optimisation of spray drying process parameters for low‐fat honey‐based milk powder with antioxidant activity

The purpose of this study was to optimise process parameters to prepare spray‐dried honey‐based milk powder containing functional properties of honey. Experimental design with temperature (180 to 200 °C), honey concentration (5–15%) and feed flow rate (8–10 rpm) as independent variables was studied to investigate the effect on product responses. Results showed that increasing the temperature resulted in powder with lower moisture, bulk density, antioxidant activity, total phenolic contents, total flavonoid contents and higher water solubility index. Increasing feed flow rate resulted in higher moisture, bulk density, antioxidant activity, reduced water solubility index, total phenolic content and total flavonoid content, whereas increasing honey concentration resulted in increase in antioxidant activity, total phenolic content and total flavonoid content. The moisture content, bulk density, water solubility index, DPPH scavenging activity, total phenolic content and total flavonoid content were 3.27%, 0.44 g cc^?1, 96.67 g g^?1, 17.45%, 2.54 GAE g^?1 powder and 1.40 RE g^?1 powder, respectively.     

Optimisation of production yield by ultrasound‐/microwave‐assisted acid method and functional property of pectin from sugar beet pulp

Response surface methodology was used to optimise pectin recovery from sugar beet pulp using ultrasound‐/microwave‐assisted acid method (UMAAM). The independent variables were microwave heating temperature, microwave heating time and solid‐to‐liquid ratio. From the results, the selected optimal conditions were 92 °C, 37 min, and solid‐to‐liquid ratio 1:30. Under these conditions, the yield and uronic acid content of the pectin (SBP1) was 26.16% and 75.38%, respectively. Compared with the sugar beet pectin (SBP2) extracted by traditional acid method, SBP1 showed a higher molecular weight, higher viscosity and emulsifying activity and stability. The possible reason was that the UMAAM could have had minimal change in the protein–polysaccharide complex structure of pectin, but significantly increased the length of polysaccharide chains compared with SBP2. These results suggested that UMAAM is an efficient method in extracting pectin and has the potential to be used in the sugar beet industry.     

Ultrasound‐assisted extraction of polyphenols from potato peels: profiling and kinetic modelling

Ultrasound‐assisted extraction (UAE) at 33 and 42 kHz has been investigated in the extraction of polyphenols from peels of two potato varieties, cream‐skinned Lady Claire (LC) and pink‐skinned Lady Rosetta (LR), commonly used in snack food production. Extraction efficacy between the UAE‐untreated (control) and the UAE‐treated extracts was assessed on the total phenolic content and antioxidant capacities (DPPH and FRAP). Application of UAE showed significantly higher recovery of phenolic compounds compared to solid–liquid extraction process alone. Lower ultrasonic frequency (33 kHz) was more effective in recovering polyphenols compared to 42 kHz ultrasonic treatment. The liquid chromatography‐tandem mass spectrometry revealed that chlorogenic acid and caffeic acid were the most prevalent phenolics in LR peels, whereas caffeic acid was dominant in LC peels. Peleg's equation showed a good correlation (R² > 0.92) between the experimental values and the predicted values on the kinetics of UAE of phenolic compounds.