Volume 16, Issue 1-2 -

This study aimed to investigate the potential of electronic nose (E-nose) to differentiate volatiles of shiitakes produced at different drying stages. Shiitakes at different drying time slots were categorized into four groups (fresh, early, middle and late stage) by sensory evaluation. E-nose was used to analyze the volatiles and compared with headspace solid phase micro-extraction combined with gas chromatography-mass spectrometry (HS/GC-MS). The principal component analysis results showed that shiitakes at each stage could be successfully discriminated by E-nose and HS/GC-MS. The differences in volatile organic compounds produced at each stage were mainly caused by sulfurs and alcohols, leading to apparent changes of sensors sensitive to sulfurs, alcohols and aromatic compounds. The discriminant models were established by partial least squares discriminant analysis and support vector machine classification, with accuracy rates of 91.25 % and 95.83 %, respectively. The results demonstrated the potential use of E-nose in classifying and monitoring shiitakes during drying process.

Potato offers numerous health benefits that have yet to be utilized by the food industry. To evaluate the use of potato as an ingredient in staple food products, various proportions of potato flour were added to wheat flour (0–50 %) to form potato–wheat flour mixtures. The mixtures were used to make dough and steamed bread that were tested based on several established quality indicators. Specifically, with increasing potato flour proportion above 20 %, dough quality indicators of extensibility, tensile resistance, fermentation volume and fermentation activity exhibited downward trends, with worsening microstructural, while steamed bread exhibited decreasing specific volume, decreasing brightness, worsening textural properties, increasing yellowness and increasing lysine content. However, for dough and steamed bread made from flour mixtures containing 10–20 % potato flour, quality indicators were not significantly different from corresponding control values (100 % wheat flour). Notably, correlation analysis indicated that tensile and fermentative dough properties significantly correlated with resulting steamed bread quality. Therefore, only data measurements for these dough indicators are needed to predict steamed bread quality, in order to reduce testing workload during evaluation of ingredient formulations for steamed bread production.

The grape pomace is a by-product from the industrial processing of grape juice, which can be used as a source of bioactive compounds. The aim of this study was to separate the phenolic compounds from grape pomace using an acidic aqueous solution with 2 % citric acid as a solvent, using both ultrasound-assisted extraction, with powers of 250, 350 and 450 W and times of 5, 10 and 15 min, and microwave-assisted extraction using powers of 600, 800 and 1,000 W and times of 5, 7 and 10 min. The results showed that for both methods of extraction, the contents of total phenolic compounds and antioxidant activity by ABTS and DPPH increased with time, and microwave at 1,000 W for 10 min corresponded to the best extraction condition. However, the contents of phenolic compounds and antioxidant activity were lower than exhaustive extraction using acidified methanol solution.

Fresh ginkgo biloba (GB) seeds are seasonal and susceptible to microbial spoilage, especially the growth of mold owing to GB seeds’ high-water content, which greatly limits their shelf life. As an efficient and special heating method, radio-frequency (RF) heating can be used to dehydrate ginkgo to preserve its nutritional value and reduce postharvest losses. However, the non-uniformity of RF heating restricts the development in industrialized application. In this study, the RF drying of GB seeds was performed to investigate the effect of RF heating on temperature. The distribution law of the entire temperature field was also observed. Using numerical simulation method, the coupling model of electromagnetic and heat transfer was established. The model was validated by the 6-min heating profile of GB seeds in a 12 kw and 27.12 MHz RF system. The model was also qualitatively validated by comparing the simulated temperature profiles on the three planes in the GB seeds with the corresponding thermal images. Quantitative validation was performed by comparing the simulated temperature of GB seeds on the three planes with experimental temperature acquired at places using thermocouples. Furthermore, the model can be effectively used to identify the distribution of electric fields in different positions and to achieve satisfactory heating uniformity.

The purpose of this study was to analyse the impact of blanching, the atmosphere of nitrogen and storage time on carotenoids content, colour and sorption properties of freeze-dried carrot. The material was stored for up to 16 weeks, in the dark, at room temperature. The colour was measured on the surface and in cross sections. As the storage time increased, there was a continual decrease in the carotenoids content in the carrot packed in atmospheric air. In the carrots packed in the atmosphere of nitrogen, no changes in carotenoid content were observed. The colour parameters correlated with the changes in the carotenoids content. The colour parameters changed on the surface and in cross sections in the same manner. During storage, a significant decrease in sorption properties of freeze-dried carrots was noted after 2 weeks of storage.

The aim of this study was to determine the effect of osmotic pre-treatment on physical and sensory properties of dried strawberry. Frozen strawberries were dehydrated in sucrose solution with/without 5 or 15 % concentrated chokeberry juice. Then, samples were dried in hybrid (convective-microwave-vacuum) and freeze-drying method. The chokeberry juice concentrate addition to the osmotic solutions had no effect on the mass transfer of dehydrated strawberries but changes in sensory properties, also after storage. Initial osmotic treatment in sucrose solution with 5 % of chokeberry juice concentrate resulted in improved colour, when 15 % addition caused the darkening of the dried strawberries. Strawberries dried by hybrid method exhibited greater hardness and brittleness than by freeze-drying, which were slightly higher evaluated in the sensory analysis. Storage for 3 months resulted in an increase in the hardness of the samples, the reduction of colour parameters and sensory quality.

Effects of agglomeration of β-carotene microencapsulated by spray drying on its stability were analysed. Mixtures of Arabic gum (GA), maltodextrin (MD), modified starch (OSA), and whey protein (WP) were used as carriers. GA + MD and OSA + MD microcapsules were subjected to agglomeration. All the samples were stored for 60 days with access to daylight. Stability of the emulsions had a significant effect on efficiency of microencapsulation but had no effect on β-carotene retention during sample storage. Among the tested samples, the highest retention of colorant characterized the samples containing GA + MD. The agglomeration process reduced the content of β-carotene in the microcapsules almost by half. However, retention of the colorant during storage of the microcapsules was increased most of all and half-life of β-carotene was significantly prolonged. Changes in L * and a * colour parameters during storage were more limited in the case of agglomerated samples.

The aim of this study was to investigate the effects of pre-treatment in ethanol solution carried out in variable time with and without ultrasound (US) assistance on convective drying kinetics, total phenolic content (TPC) and hygroscopicity of an apple. The drying time after immersion in ethanol solution was shorter up to 13.4 (without US) and 18.3 % (with US) in comparison to intact slices. The most appropriate model that described kinetics of drying was the one proposed by Sledz et al. Drying of the untreated apple resulted in a decrease of the TPC by 18 %, compared with raw apples and the pre-treatment led to further losses. The tissue after ethanol pre-treatment was less hygroscopic, which proves the possibility to maintain a characteristic texture of the dried apple with prolonged storage stability. The best quality of dried apples was obtained after 1 min of ethanolic pre-treatment with US.

The aim of this work was to study the influence of freeze-drying conditions of kiwi ( Actinidia deliciosa ) on physicochemical properties and grinding characteristics of dried fruits. Whole kiwi fruits were freeze-dried with the different pressure: 12, 20, 42, 63, 85, and 103 Pa. Dried fruit properties that underwent evaluation included color, texture, rehydration, total phenolics content, antioxidant properties and sensory analysis. Moreover, the grinding energy indices of dried kiwi were determined. The results showed that an increase in the pressure caused decreased lightness, but increased yellowness and greenness of freeze-dried kiwi. The force of kiwi penetration increased and the rehydration ability decreased with the increase in the pressure. The specific grinding energy of dried kiwi ranged from 10.1 to 13.6 kJ⋅kg −1 , whereas the average particle size of kiwi powder changed from 0.331 to 0.337 mm. The highest values of these parameters were obtained for kiwi freeze-dried with the highest pressure .

Kiwiberries ( Actinidia arguta var. Geneva) were osmotically dehydrated in sucrose, xylitol and maltitol 60 % water solutions at 30 and 50 °C. After pre-treatment, the samples were dried using convective method at 70 °C until fruits have reached a dimensionless moisture ratio (MR) of 0.02. Osmotic pre-treatment significantly improved drying kinetics during the first stage of the process. All the pre-treated samples reached water activity level ( a w ) less than 0.6 after 7 h of drying. When maltitol or xylitol was used as an osmotic agent at 30 °C, the time required for drying was reduced by 23 and 32 %, respectively. In turn, dehydration performed at 50 °C had no positive effect on the drying kinetics. The shortest drying time was obtained for the samples dehydrated in xylitol at 30 °C. In the case of these samples target MR was reached after 542 min whereas in the case of untreated samples drying lasted 810 min. The highest retention of carotenoid was observed for the samples osmotically pre-treated in maltitol solution at 30 °C and sucrose solution at 50 °C.