Dried residues from four different vegetables, viz. pea pod (pp), cauliflower waste (CW), potato peel (PP) and tomato peel (TP) were extracted using four solvents i.e., hexane, chloroform, ethyl acetate and methanol. Among the four solvents, methanolic extracts showed the highest total phenolic content (TPC) for all the four vegetable residues. Methanolic extracts were evaluated for antioxidant activities using diphenylpicryl-hydrazyl (DPPH) and reducing power assay. Tomato peel extract showed highest phenolic content of 21.0 mg GAE/g-dw and 80.8 % DPPH free radical scavenging ability, whereas potato peel extract had a low phenolic content, and it also showed the least antioxidant activity among the residues examined in this study. Total phenolic content and DPPH free radical scavenging activity in pea pods and cauliflower waste were 13.6 mg GAE/g-dw and 72 % and 9.2 mg GAE/g-dw and 70.7 %, respectively. The coefficient of determination (r(2)) for correlation between TPC and reducing power, DPPH and TPC, DPPH and reducing power for all extracts was 0.85, 0.91and 0.87, respectively, suggesting an important role of phenolics in imparting antioxidant ability. Extracts from vegetables residues therefore represent a significant source of phenolic antioxidants for use as nutraceuticals or biopreservatives.
In this study, simultaneous saccharification and fermentation (SSF) was employed to produce ethanol from 1% sodium hydroxide-treated rice straw in a thermostatically controlled glass reactor using 20 FPU gds⁻¹ cellulase, 50 IU gds⁻¹ β-glucosidase, 15 IU gds⁻¹ pectinase and a newly isolated thermotolerant Pichia kudriavzevii HOP-1 strain. Scanning electron micrograph images showed that the size of the P. kudriavzevii cells ranged from 2.48 to 6.93 μm in diameter while the shape of the cells varied from oval, ellipsoidal to elongate. Pichia kudriavzevii cells showed extensive pseudohyphae formation after 5 days of growth and could assimilate sugars like glucose, sucrose, galactose, fructose, and mannose but the cells could not assimilate xylose, arabinose, cellobiose, raffinose, or trehalose. In addition, the yeast cells could tolerate up to 40% glucose and 5% NaCl concentrations but their growth was inhibited at 1% acetic acid and 0.01% cyclohexamide concentrations. Pichia kudriavzevii produced about 35 and 200% more ethanol than the conventional Saccharomyces cerevisiae cells at 40 and 45°C, respectively. About 94% glucan in alkali-treated rice straw was converted to glucose through enzymatic hydrolysis within 36 h. Ethanol concentration of 24.25 g l⁻¹ corresponding to 82% theoretical yield on glucan basis and ethanol productivity of 1.10 g l⁻¹ h⁻¹ achieved using P. kudriavzevii during SSF hold promise for scale-up studies. An insignificant amount of glycerol and no xylitol was produced during SSF. To the best of our knowledge, this is the first study reporting ethanol production from any lignocellulosic biomass using P. kudriavzevii.
The growing interest in the substitution of synthetic food antioxidants by natural ones has fostered research in identifying new low-cost antioxidants having commercial potential. Fruits such as mango, banana, and those belonging to the citrus family leave behind a substantial amount of residues in the form of peels, pulp, seeds, and stones. Due to lack of infrastructure to handle a huge quantity of available biomass, lack of processing facilities, and high processing cost, these residues represent a major disposal problem, especially in developing countries. Because of the presence of phenolic compounds, which impart nutraceutical properties to fruit residues, such residues hold tremendous potential in food, pharmaceutical, and cosmetic industries. The biological properties such as anticarcinogenicity, antimutagenicity, antiallergenicity, and antiageing activity have been reported for both natural as well as synthetic antioxidants. Special attention is focused on extraction of bioactive compounds from inexpensive or residual sources. The purpose of this review is to characterize different phenolics present in the fruit residues, discuss the antioxidant potential of such residues and the assays used in determination of antioxidant properties, discuss various methods for efficient extraction of the bioactive compounds, and highlight the importance of fruit residues as potential nutraceutical resources and biopreservatives.
Pectin containing agricultural by-products are potential sources of a new class of prebiotics known as pectic oligosaccharides (POS). In general, pectin is made up of homogalacturonan (HG, α-1,4-linked galacturonic acid monomers) and rhamnogalacturonan (RG, alternate galacturonic acid and rhamnose backbone with neutral side chains). Controlled hydrolysis of pectin containing agricultural by-products like sugar beet, apple, olive and citrus by chemical, enzymatic and hydrothermal can be used to produce oligo-galacturonides (GalpOS), galacto-oligosaccharides (GalOS), rhamnogalacturonan-oligosaccharides (RGOS), etc. However, extensive research is needed to establish the role of POS, both as a prebiotic as well as therapeutic agent. This review comprehensively covers different facets of POS, including the nature and chemistry of pectin and POS, potential agricultural residual sources of pectin, pre-treatment methods for facilitating selective extraction of pectin, identification and characterization of POS, health benefits and important applications of POS in food and feed. This review has been compiled to establish a platform for future research in the purification and characterization of POS and for in vivo and in vitro studies of important POS, so that they could be commercially exploited.
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