The effect of oven drying on bioactive compounds, antioxidant activity, and phenolic compounds of white and red‐skinned onion slices

Effects of different preparation and cooking processes on the bioactive molecules of Allium vegetables

Allium species are among the most widely cultivated vegetables for centuries for their positive effects on human health and their variety of uses in food preparation and cooking. Preparation and cooking processes create chemical changes that can affect the concentration and bioavailability of bioactive molecules. Understanding the changes in bioactive compounds and bioactive activities in Allium vegetables resulting from preparation and cooking processes is essential for better retention of these compounds and better utilization of their health benefits. This study aimed to investigate the effects of different preparation and cooking processes on the bioactive molecules of Allium vegetables. This review concludes that bioactive compounds in Allium vegetables are affected by each preparation and cooking process depending on variables including method, time, temperature. Owing to differences in the matrix and structure of the plant, preparation and cooking processes show different results on bioactive compounds and bioactive activities for different vegetables. Continued research is needed to help fill gaps in current knowledge, such as the optimal preparation and cooking processes for each Allium vegetable.

Electrospun nanofibers based on zein and red onion bulb extract (Allium cepa, L.): Volatile compounds, hydrophilicity, and antioxidant activity

Onion is rich in bioactive and volatile compounds with antioxidant activity. However, the pungent odor of volatile compounds (VOCs) released restricts its use. The encapsulation of red onion extract by electrospinning is an alternative to mask this odor and protect its bioactive compounds. The main objective of this study was to encapsulate red onion bulb extract (ROE) in different concentrations into zein nanofibers by electrospinning and evaluate their thermal, antioxidant, and hydrophilicity properties. The major VOC in ROE was 3(2H)-furanone, 2-hexyl-5-methyl. Incorporating ROE into the polymeric solutions increased electrical conductivity and decreased apparent viscosity, rendering nanofibers with a lower average diameter. The loading capacity of ROE on fibers was high, reaching 91.5% (10% ROE). The morphology of the nanofibers was random and continuous; however, it showed beads at the highest ROE concentration (40%). The addition of ROE to the nanofibers increased their hydrophilicity. The nanofibers' antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl, nitric oxide, and hydroxyl radicals ranged from 32.5% to 57.3%. The electrospun nanofibers have the potential to protect and mask VOCs. In addition, they offer a sustainable alternative to the synthetic antioxidants commonly employed in the food and packaging industry due to their antioxidant activities.

Effects of different re-fermentation methods on the quality characteristics of kombucha beverages

The effects of different re-fermentation methods on the quality characteristics of kombucha beverages were investigated. The quality characteristics of kombucha beverages included the basic physicochemical indicators (pH, total acidity, reducing sugar, total sugar, organic acids, total phenolic compound, total flavonoid compound), antioxidant activity, volatile flavor substance and sensory evaluation of the beverages. The results showed the re-fermentation methods including the mixed fermentation and the step-by-step fermentation significantly decreased total acidity and various organic acids (P < 0.05) than traditional kombucha with no re-fermentation. In addition, the contents of total phenol compounds and total flavonoid compounds for the step-by-step fermentation were 184.70 and 338.33 mg/L respectively, and were higher compared with mixed fermentation and traditional kombucha with no re-fermentation. The antioxidant activity in the step-by-step fermentation was much stronger than that of mixed fermentation and traditional kombucha with no re-fermentation. Moreover, there were 53 kinds of volatile flavor compounds produced in the step-by-step fermentation, 14 of them were unique with good sensory quality. In conclusion, the re-fermentation methods for traditional kombucha (the step-by-step fermentation and mixed fermentation) had more active ingredients and better sensory quality, and the step-by-step fermentation was better than mixed fermentation.

The Influence of Non-Optimal Rearing Conditions and Substrates on the Performance of the Black Soldier Fly (Hermetia illucens)

Simple Summary

The black soldier fly is one of the insect species most frequently reared as an alternative protein source. Even though many advances have been made in the last decade regarding environmental and process conditions, there are still several gaps that can delay the upscaling of industrial production systems. One of such gaps is related to the effect of suboptimal feeding regimes of mono-waste streams. This research aims to assess the development and bioconversion behaviour of black soldier fly larvae under suboptimal conditions. It was observed that specific types of vegetable and fruit wastes, such as apple, spinach and grape pomace, may contribute to achieve low insect biomass yields and, thus, reduce the efficiency of industrial operations.

Abstract

Among the insect species reared as alternative protein sources, Hermetia illucens (black soldier Fly, BSF) has shown a huge potential mostly due to its high protein content, its bioconversion rates, and versatility in using different feeding substrates. Insect rearing may use continuous or batch feeding regimes and, among the used substrates, supermarket feedstock waste has gained recent interest under a circular economy perspective, but several uncertainties remain regarding the heterogeneity and the potential effects of the quantity and quality of these substrates on BSF larvae (BSFL) development. In this experimental work, five replicates of a hundred BSFL were fed in a continuous feeding regime, using seven different isolated vegetables as substrates (wheat bran, pumpkin, apple, grape pomace, red onion, red cabbage, and spinach), at three different temperatures (20, 25, and 30 °C) and two substrate moisture conditions (natural and 70% substrate moisture), until 50% of the larvae achieved the prepupal stage. BSFL performance and bioconversion parameters were evaluated. Our results show that some substrates should be avoided when rearing Hermetia illucens on feedstocks. Among these, apple feed led to poorer and slower development performances with more than 100 days of larval stage, while grape pomace and spinach showed higher mortality rates, which may be due to some anti-nutritional compounds. Larvae fed on pumpkin, red cabbage, and red onion presented good bioconversion results with higher values of efficiency of conversion of digested feed between 14.4 and 25. This work delivers relevant results for black soldier fly reared on a continuous feeding system using vegetable feedstock substrates and their potential trade-offs.

Boiling Technique-Based Food Processing Effects on the Bioactive and Antimicrobial Properties of Basil and Rosemary

Rosemary (Rosmarinus officinalis) and basil (Ocimum sanctum Linn) are mostly used as herbal teas, made by steeping whole or ground herbs in boiling water. Hence, it is important to know the effect of boiling time on the bioactivity of these herbs. The effect of different boiling times (5, 10, and 15 min) on the antioxidant and antimicrobial properties, and some selected phenolic compounds of these herbs was examined in this study. Experimental results revealed that basil displayed the highest total polyphenol content (TPC), total flavonoid content (TFC), and antioxidant activity when it was boiled for 5 min, and the lowest TPC was obtained when it was boiled for 15 min. On the other hand, rosemary had the highest TPC, TFC, and antioxidant potential after being boiled for 15 min, while it had the lowest after being boiled for 5 min. There was no growth inhibition of rosemary extracts against gram-negative bacteria, whereas higher growth inhibition was observed against gram-positive bacteria. The MIC and MBC of rosemary ethanolic extract against Listeria monocytogenes were 5 and 5 mg/mL and against B. subtilis were 10 and 10 mg/mL, respectively. While MIC and MBC of methanolic extract against L. monocytogenes were 5 and 5 mg/mL and against Bacillus subtilis were and 5 and 5 mg/mL, respectively. Salicylic acid was the most abundant (324.7 mg/100 g dry weight (dw)) phenolic compound in the rosemary sample boiled for 5 min, and acetyl salicylic acid was the most abundant (122.61 mg/10 g dw) phenolic compound in the basil sample boiled for 15 min.

Investigation of the Potential Use, Phytochemical and Element Contents of Acacia Plant Seeds Grown in Wild Form, Considered as Environmental Waste

In this study, the effect of altitude on oil amounts, antioxidant activity, polyphenol content and mineral contents of Acacia seeds collected from two different locations (up to 1100 m above sea level) was investigated. Total carotenoid and flavonoid contents of Acacia seeds were detected as 0.76 (Konya) and 1.06 µg/g (Taşucu-Mersin) to 1343.60 (Konya) and 184.53 mg/100 g (Taşucu-Mersin), respectively. Total phenol contents and antioxidant activity values of Acacia seeds were identified as 255.11 (Konya) and 190.00 mgGAE/Taşucu-Mersin) to 64.18% (Konya) and 75.21% (Taşucu-Mersin), respectively. The oils extracted from Acacia seeds in Konya and Mersin province contained 62.70% and 70.39% linoleic, 23.41% and 16.03% oleic, 6.45%and 6.04% palmitic and 2.93% and 4.94% stearic acids, respectively. While 3,4-dihydroxybenzoic acid amounts of seeds are determined as 3.89 (Konya) and 4.83 mg/100 g (Taşucu-Mersin), (+)-catechin contents of Acacia seeds were identified as 3.42 (Konya) and 9.51 mg/100 g (Taşucu-Mersin). Also, rutintrihydrate and ferulic contents of Acacia seeds were found as 23.37 (Konya) and 11.87 mg/100 g (Taşucu-Mersin) to 14.74 mg/100 g (Konya) and 1.12 mg/100 g (Taşucu-Mersin), respectively. Acacia seeds collected from Konya and Mersin contained 4003.75 and 3540.89 mg/kg P, 9819.12 and 16175.69 mg/kg K, 4347.47 and 5078.81 mg/kg P, 2195.77 and 2317.90 mg/kg Mg, 1015.75 and 2665.60 mg/kg S and 187.53 and 905.52 mg/kg Na, respectively.

Dehydrated at Different Conditions and Powdered Leek as a Concentrate of Biologically Active Substances: Antioxidant Activity and Phenolic Compound Profile

This study aimed to analyze the antioxidant activity, phenolic acid profile, color changes, and chemical composition of dried and powdered leek (Allium porrum). Leek was divided into white shaft (WH) and green shaft (GR) and subjected to drying by different methods—convection drying, vacuum drying, and freeze-drying (FD)—at a temperature of 60 °C. A sample freeze-dried at a temperature of 20 °C was used as control. Analyses of the dried leek samples revealed that GR contained a higher amount of ash, protein, fat, fiber, phenolic acids, and flavonoids, and exhibited higher antioxidant capacity compared to WH. The dominant phenolic acid in WH was p-cumaric acid followed by synapic and protocatechuic acids. GR had a several-fold higher content of phenolic acids than WH, with ferulic acid being dominant (about 85% of the total phenolic content). It was also observed that a higher drying temperature resulted in the degradation of phenolic compounds and reduced the antioxidant properties of leek shafts. Most importantly, FD under a temperature of 60 °C caused a similar degree of degradation of biologically active compounds as air drying. An increase in drying temperature was associated with a slight decrease in the lightness of GR, whereas in the case of WH no significant change in this parameter was observed.

Recent Advances in Bioactive Compounds, Health Functions, and Safety Concerns of Onion (Allium cepa L.)

Onion (Allium cepa L.) is a common vegetable, widely consumed all over the world. Onion contains diverse phytochemicals, including organosulfur compounds, phenolic compounds, polysaccharides, and saponins. The phenolic and sulfur-containing compounds, including onionin A, cysteine sulfoxides, quercetin, and quercetin glucosides, are the major bioactive constituents of onion. Accumulated studies have revealed that onion and its bioactive compounds possess various health functions, such as antioxidant, antimicrobial, anti-inflammatory, anti-obesity, anti-diabetic, anticancer, cardiovascular protective, neuroprotective, hepatorenal protective, respiratory protective, digestive system protective, reproductive protective, and immunomodulatory properties. Herein, the main bioactive compounds in onion are summarized, followed by intensively discussing its major health functions as well as relevant molecular mechanisms. Moreover, the potential safety concerns about onion contamination and the ways to mitigate these issues are also discussed. We hope that this paper can attract broader attention to onion and its bioactive compounds, which are promising ingredients in the development of functional foods and nutraceuticals for preventing and managing certain chronic diseases.