Effect of the Drying Method and Storage Conditions on the Quality and Content of Selected Bioactive Compounds of Green Legume Vegetables

This study aimed to determine the effect of the drying method (freeze-drying, air-drying), storage period (12 months), and storage conditions (2-4 °C, 18-22 °C) applied to two legume species: green beans and green peas. The raw and dried materials were determined for selected physical parameters typical of dried vegetables, contents of bioactive components (vitamin C and E, total chlorophyll, total carotenoids, β-carotene, and total polyphenols), antioxidative activity against the DPPH radical, and sensory attributes (overall quality and profiles of color, texture, and palatability). Green beans had a significantly higher content of bioactive components compared to peas. Freeze-drying and cold storage conditions facilitated better retention of these compounds, i.e., by 9-39% and 3-11%, respectively. After 12 months of storage, higher retention of bioactive components, except for total chlorophyll, was determined in peas regardless of the drying method, i.e., by 38-75% in the freeze-dried product and 30-77% in the air-dried product, compared to the raw material.

Effect of dehydration and pulsed light treatment on decontamination of minced onions: Microbial safety and physicochemical properties

Microbial contamination of dehydrated onion products is a challenge to the industry. The study focused on opting for a suitable drying condition for minced onion and exploring the decontamination efficacy of pulsed light (PL) treatment conditions for the dehydrated product. The minced onions were hot air dried at 55-75°C for 280 min. The drying condition selected was 195 min at 75°C with a final water activity of 0.5 and moisture content of 7% (wet basis [w.b.]). The weight losses, browning indexes (BI), shrinkage volumes (%), and thiosulfinate content were considered. The dehydrated product was exposed to PL treatment corresponding to an effective fluence range of 0.007-0.731 J/cm2. A fluence of 0.444 J/cm2 (1.8 kV for 150 s) achieved 5.00, 3.14, 2.96, and 2.98 log reduction in total plate count, yeast and mold count, Bacillus cereus 10876, and Escherichia coli ATCC 43888, respectively. The PL-treated sample (0.444 J/cm2) produced a microbially safe product with no significant difference in the moisture contents (%w.b.) and water activity (aw) from the untreated dehydrated sample. Further, a 30.9% increase in the BI and a 4.25% depletion in thiosulfinate content were observed after PL treatment. An optimum drying combination (75°C for 195 min) of minced onion followed by decontamination using pulsed light treatment at 0.444 J/cm2 fluence satisfies the microbial safety and quality. PRACTICAL APPLICATION: Dehydrated minced onion can be used for dishes requiring low water content and short cooking time. It is helpful during shortages, high price fluctuations, and famines.

Comparative Analysis of Polyphenol Content and Antioxidant Activity of Different Parts of Five Onion Cultivars Harvested in Korea

Onions are typically consumed as the bulb, but the peel and root are discarded as by-products during processing. This study investigated the potential functional use of these by-products by analyzing the polyphenols, antioxidant compounds, and antioxidant activity contained in onions. In this study, the bulb, peel, and root of five onion cultivars ('Tank', 'Bomul', 'Gujji' 'Cobra', and 'Hongbanjang') harvested in Korea were investigated. Caffeic acid and quercetin were most abundant in the peel, whereas methyl gallate was the predominant polyphenol in the bulb. Both DPPH and ABTS radical scavenging activity were higher in onion peel and root than in the bulb. These findings suggest that onion peel and roots, which are often discarded, have abundant antioxidant substances and excellent antioxidant activity. This study provides basic data for the future use of onion peel and roots as functional ingredients with high added value.

The effect of different pretreatments followed by enzyme reaction on preparing shape-retaining softened burdock

To prepare texture-softened burdock that maintains its original shape, the effect of three different pretreatments before pectinase reaction (ENZ) up to 3 h: heating and drying (HD), freeze-thawing after heating and then drying (HFTD), or freeze-drying after heating (HFD) was compared. The hardness of raw burdock could be decreased by 15% after ENZ up to 3 h. The order of hardness by pretreatment was HFD (-93.3%) < HFTD (-80.7%) < HD (-52.8%) < R (raw), implying that the burdock could be softened by pretreatment itself. By the combination of pretreatment and ENZ, HFTD-ENZ for 3 h or HFD-ENZ over 2 h produced excellent softening. Hardness less than 2.0 × 10⁴ (N/m²) was obtained by HFD followed by ENZ over 2 h, and this could possibly be ingested by the tongue without chewing. More chlorogenic acid was also detected with those samples.

Volatile composition and sensory characteristics of onion powders prepared by convective drying

Volatile composition and sensory characteristics of onion powders prepared by convective drying at different temperatures (50, 70, and 90°C) were investigated. Dipropyl disulfide was the major volatile compound in fresh onion (77.70% of total volatile compounds). However it was considerably lost during drying, reaching 6.93-32.25µg/g solids. Dipropyl disulfide showed a positive correlation with green sensory attribute perceived by descriptive sensory analysis. Thiophenes, which were responsible for caramel and sweet attributes, were produced by drying especially when the drying temperature was high. Aldehydes, another type of volatile compound found in fresh onion, showed a positive correlation with humidity. The aldehyde content in dried onion was the highest at the lowest drying temperature, possibly because the aldehydes were produced by the residual enzymes in fresh onion. Using a low temperature for drying was ideal to retain the aroma of fresh onion.