1,721,009 research outputs found
Hot Air Drying Optimization and Modelling of Peach Slices
No full textPeach (Prunus persica) is a highly perishable fruit with short shelf-life and susceptible to mechanical damage during harvest and post-harvest operations such as sorting, processing, packaging, and transport. Therefore, converting peaches into dehydrated products will not only reduce their post-harvest losses but also retain their nutritional and sensory qualities.
Drying is widely used in food industry, to prolong the shelf life, improve the food stability and reduce the quality changes. In this context, drying combined with a pretreatment (chemical or physical) is an efficient method for reducing physico-chemical and nutritional changes and for improving preservation. In this study, the influence of hot air drying temperature and an innovative dipping solution (carbohydrate/salt diluted solution of trehalose, sucrose and NaCl) on drying kinetics, quality parameters (i.e. colour, shrinkage, antioxidant activity), volatile aroma compounds (VOCs) and rehydration behavior of peach slabs was investigated. Drying experiments were conducted in a convective drier at 45, 50, 55 and 60 °C with a fixed air velocity of 2.3 m/s. Peach fruits were subjected to GC/MS analysis to identify the volatile organic compounds (VOCs), extracted using a SPME fiber of divinylbenzene/carboxen/polydimethylsiloxane. Afterwards, all dried slabs were rehydrated in distilled water at 30 °C. The obtained results revealed that pre-treatment solution not only affected the drying kinetics of peach slabs, it also improved the quality attributes. The combination of pre-treatment and higher drying temperature (60°C) exhibited shorter drying time, better color retention, less shrinkage, and higher rehydration capacity.
The major VOCs of fresh peach were: benzaldehyde (553 μg/kg d.b.); 4-decalactone (293 μg/kg d.b.); (E)-2-hexenal (131 μg/kg d.b.), cis-3-hexenylacetate (129 μg/kg d.b.); isopentanoic acid (87 μg/kg d.b.) and 2-phenylethylalcohol (75 μg/kg d.b.). Anyway, the contribution of the substances to the odor note of the fruit depended not only in the quantities of the compounds, but also mainly on their perception threshold. VOCs with odor activity value (OAV) > 1, considered to contribute to the aroma of the peach, were: 4-decalactone (OAV=2.92); benzaldehyde (OAV=1.73); (E)-2-hexenal (OAV=1.60) and 2-phenylethylalcohol (OAV=1.21)
All the compounds with the odorous impact of the peaches were significantly reduced after drying, modifying fruits odorous profiles. On the other hand, several new compounds were formed, because of various chemical transformations, including the Maillard reaction. The dried samples compared to fresh peaches showed an increase in aldehydes, ketones and especially terpenes and acids. The highest concentration of these compounds was higher in TR samples. In particular, the concentration of nonanal, described as having partially green aromas, with citrus characteristics, had in all dried samples OAV > 1, with maximum values in TR 50°C (OAV=2.43).
Furthermore, a diffusion model including the effect of shrinkage was developed to describe the drying process of both untreated and treated peaches. The experimental data of moisture ratio during drying were well predicted by the diffusion model developed. The calculated values of effective diffusivity increased with increasing drying temperature. Moreover, the treated peach slices had higher moisture diffusivity values in comparison with the untreated peach samples. The calculated values of activation energy indicated that a little less energy is required for the drying of treated peach samples respect to untreated. This behaviour showed that the pre-treatment aids moisture diffusion and evaporation and thus reduces slightly the energy involved in the drying process.
In conclusion, overall results showed that for treated peach slabs drying conditions of 60°C air temperature are the optimum for the product quality in terms of drying kinetics, colour, shrinkage, rehydration behaviour and aroma
The Influence of Abrasive Pretreatment on Hot Air Drying of Grape
Full text linkThe drying of grapes is a more complex process compared to the dehydration of other agricultural
materials due to the necessity of a pretreatment operation prior to drying. Grape drying to produce
raisins is a very slow process, due to the peculiar structure of grape peel, that is covered by a
waxy layer. Its removal has been so far carried out by using several chemical pre-treatments.
However, they cause heterogeneity in the waxes removal and create microscopic cracks. In this
paper an abrasive pretreatment for enhancing the drying rate and preserving the grape samples is
proposed. Two cultivars of grape were investigated: Regina white grape and Red Globe red grape.
The drying kinetics of untreated and treated samples were studied using a convective oven at 50 ̊C.
Fruit quality parameters such as sugar and organic acid contents, shrinkage, texture, peel damage
(i.e. by SEM analysis) and rehydration capacity were studied to evaluate the effectiveness of abrasive
pretreatment on raisins. Abrasive pretreatment contributed to reduce drying time and rehydration
time. The treated and untreated dried grapes were significantly different (p < 0.05) in
sugar and in tartaric acid content. On the contrary, no significant differences (p < 0.05) in malic
and citric acids and in texture properties between untreated and treated samples were observe
Combined Pretreatment for Enhancing Quality of Dried and Rehydrated Eggplant
No full textA combined pretreatment of trehalose (0.5 %) and NaCl (0.5 %) solution was applied prior to drying eggplant to reduce shrinkage, browning and loss of polyphenols. Drying behaviour of eggplant slabs was experimentally examined in a convective dryer at temperatures of 50, 60 and 70 °C and at 2.3 m/s air velocity. Then the effects of pretreatment and drying temperature on the quality of the eggplant slabs in terms of microstructure, porosity, colour, total phenolic content, rehydration ratio and texture were investigated. It was noted that the pretreated eggplants (TR) dried more rapidly than the untreated ones (UTR) with a reduction of up to 1/4 of drying time. After drying at 50 and 60 °C, they showed no significant differences (p < 0.05) in terms of White index compared with fresh eggplant (78.59 ± 0.63). They had higher total phenolic content (19.86 and 18.24 mg/g (db), respectively) than the UTR ones (11.91 and 12.89 mg/g (db)), but only for the TR samples at 50 °C the value is not statistically different (p < 0.05) from the fresh ones (20.00 mg/g (db)). The pretreatment can hold also a higher porosity (85, 86 % at 50 and 60 °C, respectively) than the UTR ones (78, 82 %), but scanning electron microscopy (SEM) images indicated a total damage structure of the UTR samples. On the contrary, after the pretreatment, the porous structure was more uniform with more not lacerated cellular walls. Hence, the main effect of pretreatment was of protecting the microstructure of the eggplants by reinforcing the cell walls and to reduce the resistance of the water evaporation by avoiding the structural changes. After rehydration, the pretreated samples absorbed more water (rehydration ratio had almost doubled) than the untreated ones and showed lower firmness (95,500 Nm−1) compared with the untreated ones (132,000 Nm−1)
Influenza di fitofarmaci innovativi sulla conservabilità di cultivar di Lactuca sativa.
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Microstructural Approach Application for Morphological Change Determinations of Grapes during Drying
Full text linkGrape dehydration is practiced widely in the food industry with large yields of sultanas produced globally. This paper proposes an investigation into the microstructure changes of grapes as they are dried by imaging specimens at intervals during dehydration at two temperatures using scanning electron microscopy. Two main methods were developed to obtain the complex boundaries of cells present in grape tissue in over 36 SEM images. Segmentation of the binary image using an adapted watershed function obtained the most consistent and accurate morphological shape. This was compared to a secondary method which used Canny’s edge detection function, morphological closing and skeletonizing to outline the cellular microstructure. MATLAB was utilised to convert these boundaries into measurable areas so that quantitative data on average cell area, perimeter and cell axis lengths were acquired. It was found that over the drying time, the cell area and perimeter were reduced as expected. Some variability in the data was clear due to only single samples being analysed for each temperature and time combination. Trends in cell perimeter, diameter and shape will be used to demonstrate relationships between morphological structure, drying temperature, and duration. Detailed images of the microstructure were obtained, and a unique image processing algorithm was developed to quantitatively analyse the properties of this microstructure. The development of automatic image processing techniques and algorithms will enable quantitative data to be extracted from any image and extend to any plant/food material
Biochemical, antioxidant properties and antimicrobial activity of different onion varieties in the Mediterranean area
No full textOnion (Allium cepa L.) is a very important vegetable crop cultivated worldwide. The bulb is a major source of phytochemicals useful for human health and rich in sulphur compounds responsible for their typical odour and flavour. In this study, we investigated the volatile compounds and biochemical properties besides the antimicrobial activity of onion Montoro and Alife varieties, and of two ecotypes of Vatolla variety (spinning top and tapered shape), cropped in the southern Mediterranean area (Italy). For all investigated onions, the organosulphur compounds, mainly di- and trisulfides, are the most abundant compounds. Alife variety showed higher polyphenols amount (8.2 GAE mg/g dw) with respect to the lowest one (3.9 GAE mg/dw g) in spinning top Vatolla, as well as an higher antioxidant activity (42.37 μmol TE/g dw) about two-fold higher than those detected in the other varieties. All the onions showed low pungency level, confirming their popular classification as a sweet onion. The total content of soluble sugars ranged from 461 to 624 mg/g dw; malic acid was the major organic acid in Alife and Montoro varieties instead for both Vatolla ecotypes citric acid was the most abundant ones. The biochemical characterization highlighted the three onion varieties as a good source of bioactive compounds. The antimicrobial activity of the onion extracts pointed out an effective action against three Gram-positive species (B. cereus, L. innocua, S. aureus) and P. aeruginosa; consequently, they could represent a new source of natural antimicrobial agents
Effect of abrasive pretreatment on hot dried goji berry
Full text linkGoji (Lycium barbarum L.) is a Solanaceous deciduous shrub that grows in China, Tibet and other parts of Asia. Nowadays, goji berries are known as being very rich in nutrients with high antioxidant capacity, fact for which they were included in the novel category of "superfruits". Goji berries contain high amounts of antioxidants, carotenoids, vitamin A and zeaxanthin. Most of goji berries produced are dried because they are very delicate fruits. Drying process improves fruit stability, since it decreases considerably the water activity of the food, reduces microbiological and enzymatic activity and minimizes physical and chemical reactions during storage. However, drying of goji berries can be difficult due to the wax layer surrounding the fruit and the health properties may be reduced by long exposure to high temperatures.
In this study, a physical wax abrasive pretreatment was used to carefully remove the wax layer and reduce drying time. The abrasion of the goji peel was carried out in a motorized drum lined inside with sandpaper. The rotating time was optimized to reduce the damage to the fruits. The drying characteristics of pretreated and untreated fruits were studied using a convective oven at 60 degrees C and air velocity of 2.1 m/s.
The drying kinetics and fruit quality parameters such as colour, sugars and antioxidant activity were evaluated before and after drying. The results showed that the dried fruit were obtained in less time when they were pretreated (from 21 h for untreated samples to 15 h for pretreated samples), preserving better the colour, increasing the antioxidant activity and maintaining the same sugar content with respect to the untreated case
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