Effect of enzymatic debittering on antioxidant capacity and protective role against oxidative stress of grapefruit juice in comparison with adsorption on exchange resin

Debittering of Grape Juice by Electrospun Nylon Nanofibrous Membranes: Impact of Filtration on Physicochemical, Functional, and Sensory Properties

The effect of electrospun nylon-6 nanofibrous membranes (NFMs) on the concentration of bitter compounds and antioxidants of grapefruit juices during dead-end filtration processes was studied. Filtration experiments with aqueous standard solutions of different molecules showed that NFMs retain low molecular weight antioxidants (i.e., ascorbic and caffeic acids) only at early filtration stages, whereas they remove bitter glycosylated phenolics (i.e., naringin and narirutin) at a more stable ratio, variable according to the membrane thickness. Experiments with fresh grapefruit juice of two varieties (pink and yellow) showed that NFM-filtration reduces (17 to 30%) flavanones associated with the immediate bitterness and allows for the complete removal (>99.9%) of limonin, responsible for the persistent bitterness of many citrus juices. In contrast, the same process causes a lower loss of ascorbic acid (5%) and does not affect acidity, nor sugar concentration. The results confirmed that NFMs feature permselectivity towards bitterness-related compounds. This work highlights the NFM potential as filter devices for the selective reduction of the bitter terpenoid (limonin) and glycosylated flavonoids (naringin and narirutin) from grape juice citrus juices in the production of industrially-relevant beverages.

Increasing Antioxidant Activity in Food Waste Extracts by β-Glucosidase

Research background

Food by-products such as onion peels and olive leaves are rich in bioactive compounds applicable as natural and low-cost sources of antioxidants. Still, these compounds mainly exist in glycosylated form. Often, hydrolysis of glycoside compounds increases their antioxidant activity and health benefits. However, not many studies have been done concerning the β-glucosidase effect, specifically from Aspergillus niger, on glycosylated compounds within these by-products. Also, changes in the antioxidant activity of the mentioned by-products under the effect of β-glucosidase have not been reported yet. Therefore, this study considers the effect of A. niger β-glucosidase on glucoside compounds and the antioxidant activity of onion peel and olive leaf extracts.

Experimental approach

The antioxidant activity of the extracts was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. Also, glucose, total phenolic and flavonoid contents were measured. Moreover, TLC and HPLC analyses were performed before and after the enzymatic hydrolysis.

Results and conclusions

The obtained results showed an increase in the extract antioxidant activity after treatment. Also, β-glucosidase increased the glucose content of the extracts. The thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC) results showed the β-glucosidase efficacy to hydrolyze quercetin glucosides in onion peel extract, and the quercetin concentration increased from (0.48±0.04) mg/mL in the untreated extract to (1.26±0.03) mg/mL in the treated extract (0.5% m/V) after 3 h of enzymatic hydrolysis at 45 °C. Also, the content of quercetin-3-O-glucoside increased considerably from (1.8±0.1) to (54±9) µg/mL following the enzyme treatment. Moreover, oleuropein in olive leaf extract (1% m/V) was hydrolyzed completely from (0.382±0.016) to 0 mg/mL by β-glucosidase for 24 h at 50 °C.

Novelty and scientific contribution

This study showed that A. niger β-glucosidase, as a stable enzyme, hydrolyzed quercetin and oleuropein glycosides in onion peel and olive leaf extracts. Thus, A. niger β-glucosidase is a good candidate for processing the food waste and extracting valuable bioactive compounds. Also, the treated extracts with higher antioxidant and biological activity, and without bitter taste can be applicable as potent, natural and cost-effective antioxidants in the food industry.

A Comparative Study on the Debittering of Kinnow (Citrus reticulate L.) Peels: Microbial, Chemical, and Ultrasound-Assisted Microbial Treatment

Kinnow mandarin (Citrus reticulate L.) peels are a storehouse of well-known bioactive compounds, viz., polyphenols, flavonoids, carotenoids, limonoids, and tocopherol, which exhibit an effective antioxidant capacity. However, naringin is the most predominant bitter flavanone compound found in Kinnow peels that causes their bitterness. It prohibits the effective utilization of peels in food-based products. In the present study, a novel approach for the debittering of Kinnow peels has been established to tackle this problem. A comparative evaluation of the different debittering methods (chemical, microbial, and ultrasound-assisted microbial treatments) used on Kinnow peel naringin and bioactive compounds was conducted. Among the chemical and microbial method; solid-state fermentation with A. niger led to greater extraction of naringin content (7.08 mg/g) from kinnow peels. Moreover, the numerical process optimization of ultrasound-assisted microbial debittering was performed by the Box–Behnken design (BBD) of a response surface methodology to maximize naringin hydrolysis. Among all three debittering methods, ultrasound-assisted microbial debittering led to a greater hydrolysis of naringin content and reduced processing time. The optimum conditions were ultrasound temperature (40 °C), time (30 min), and A. niger koji extract (1.45%) for the maximum extraction rate of naringin (11.91 mg/g). These debittered Kinnow peels can be utilized as raw material to develop therapeutic food products having a high phytochemical composition without any off-flavors or bitterness.

Ultrasound aided debittering of bitter variety of citrus fruit juice: Effect on chemical, volatile profile and antioxidative potential

In the present study, sonication assisted debittering of pomelo fruit juice was carried out and the effect of sonication along with resin/enzyme on the chemical, phytochemical and volatile composition of juice was also investigated. The optimum conditions for sonication coupled debittering using resin were 50 kHz, 2 min, and 45 ℃ while 50 kHz, 60 min, and 60 ℃ were obtained for enzyme hydrolysis. Sonication treatment not only reduced the debittering time but also enhanced the adsorption and hydrolysis of naringin by 17% and 20% in resin and enzyme respectively. In addition, enzymatic activity was also improved and weakened C-O bonds in naringin. At the same time, sonication significantly affected the bioactive compounds of juice, chemical composition, and volatile compounds of juice. Flavor compounds including octanal, linalool, citral, and ethyl butyrate were enhanced by sonication-assisted enzymatic treated juice.

Variation of bitter components of the asparagus juices during lactic acid bacteria fermentation

To investigate the bitterness status of asparagus juices during lactic acid fermentation, Limosilactobacillus fermentum Xd, Lacticaseibacillus paracasei Yd, Lactiplantibacillus plantarum 5-7-3, and their various combinations were used for single and mixed fermentation of asparagus juices. The fermentation characteristics and variation of the main bitter substances were studied. For the single and cofermented samples, the viable counts, pH value, and acidity were ranged from 8.33-8.65 lg CFU/mL, 3.58-3.86, and 6.29-6.52 g/kg, respectively. By sensory evaluation, the bitterness of every fermented sample was continuously reduced by at least 77% during fermentation, and the corresponding content of total saponins, flavonoids, and 9 bitter amino acids showed varying degrees of declination. These results suggested that it was feasible to develop novel low-bitter asparagus juices fermented by the lactic acid bacteria used in this study.

Novel Strategy of Mussel-Inspired Immobilization of Naringinase with High Activity Using a Polyethylenimine/Dopamine Co-deposition Method

Mussel-inspired surface chemistry is recognized as a simple, efficient, and mild surface modification method and has become a research hotspot in many fields. In this study, polyethylenimine/dopamine was coated on the surface of SBA-15 using a co-deposition method, making it possible to immobilize naringinase with high activity and operation stability. The optimal modification and immobilization conditions as well as enzyme properties were investigated. The naringinase activity can reach up to 753.78 U/g carrier, which was much higher than those of the previous works. Besides, the residual naringinase activity still kept 78.91% of the initial activity after one month of storage and maintained 60.79% after 8 cycles. Therefore, the strategy of mussel-inspired enzyme immobilization could be recognized as a promising and universal enzyme immobilization method, with the advantages of high relative enzyme activity, enzyme carrying rate, enzyme activity recovery rate, and good reusability and storage stability.

Outgoing and potential trends of composition, health benefits, juice production and waste management of the multi-faceted Grapefruit Citrus Χ paradisi: A comprehensive review for maximizing its value

Grapefruit (GF) Citrus Χ paradisi Macfad (F. Rutaceae) is one of the major citrus fruits that encompass a myriad of bioactive chemicals and most unique among citrus fruits. Nevertheless, no study has yet to assess comprehensively its multitudinous constituents, health benefits, and valuable waste products. Hereto, the present review provides an updated comprehensive review on the different aspects of GF, its juice production, waste valorization, enhancement of its byproducts quality, and compared to other citrus fruits. Grapefruit uniqueness among other citrus fruits stands from its unique taste, flavor, and underlying complex chemical composition. Despite limonene abundance in peel oil and grapefruit juice (GFJ) aroma, nootkatone and sulfur compounds are the key determinants of its flavor, whereas flavanones contribute to its bitter taste and in conjunction with limonoids. Different postharvest treatments and juice processing are reviewed and in context to its influence on final product quality and or biological effects. Flavanones, furanocoumarins, and limonoids appear as the most prominent in GF drug interactions affecting its metabolism and or excretion. Valorization of GF peel is overviewed for its utilization as biosrobent, its oil in aromatherapy, limonene as antimicrobial or in cosmetics, fruit pectin for bioethanol production, or as biosorbent, and peel phenolics biotransformation. The present review capitalizes on all of the aforementioned aspects in GF and further explore novel aspects of its juice quality presenting the full potential of this valued multi-faceted citrus fruit.

Effect of cold plasma on blueberry juice quality

This work focusses on the effects of cold plasma, a novel, non-thermal technology, on the quality of blueberry juice, such as inactivation of Bacillus, anthocyanins, phenolics, vitamin C, antioxidant activity and color change. Oxygen concentration (0, 0.5% and 1%) of ionized gas was firstly confirmed to be the main factors for CP treatment, besides treatment time (2, 4 and 6 min). The increment of treatment time and oxygen concentration significantly promoted an increasing trend of death for Bacillus. Compared with thermal treatment, the content of phenolics was significantly increased by CP treatment, and also CP treatment could better keep the original color of blueberry juice. In terms of anthocyanin and vitamin C, relatively shorter exposure time to CP was more suggested. In antioxidant tests, increment of oxygen concentration resulted in the increasing trends of antioxidant activity in DPPH and ABTS assays.

Debittering of lemon juice using surface molecularly imprinted polymers and the utilization of limonin

In this work, surface molecularly imprinted polymers (SMIPs) were prepared as a specific sorbent to remove the limonin from the lemon juice for the first time, and then the MIPs containing limonin were directly made into a water-soluble gel to treat inflammation of mice. The resulting polymers were characterized by scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectrometer spectra. And the polymerization conditions and adsorption performances of the resultant nanomaterials were further investigated in detail. Results showed that the MIPs have higher adsorption capacity (27.72 mg/g) compared with surface molecularly non-imprinted polymers (NIPs) (8.12 mg/g). The selectivity experiment indicated that the polymers had excellent selective recognition for limonin and the selectivity factors were calculated as 2.75 and 1.83 for nomilin and obakunone, respectively. The MIPs were successfully used as adsorbent for selectively removing limonin from lemon juice and the MIPs extracted almost all the limonin from lemon juice according to the HPLC results. Furthermore, the MIPs with limonin were processed into water-soluble gel, which can be used to reduce the inflammation and enhance wound healing of model mice.

Response surface optimization of conditions for debittering of white mahlab (Prunus mahaleb L.) juice using polystyrene resins

In the current study, debittering of white mahlab (Prunus mahaleb L.) juice using polystyrene resins was investigated and optimized using the Box-Behnken response surface methodology. The effects of independent variables including resin type (cation exchange resin, anion exchange resin, and 50:50 cation/anion exchange resin), resin dosage (0.05, 0.075, and 0.1 g/mL) and agitation speed (50, 150, and 250 rpm) on total phenolic content, total flavonoid content, total anthocyanin content (TAC), antioxidant activity, and bitterness of white mahlab juice were studied. Effects of resin type and dosage were found to be significant (p < 0.05) for all responses. A dosage of 0.05 g/mL of the anion exchange resin and an agitation speed of 250 rpm were selected as the optimum conditions based on minimum bitterness (2.42) and maximum TAC (0.018 g/mol). We could conclude that the anionic resin can greatly reduce the intensity of bitterness and maintain the composition and characteristics of the P. mahaleb juice.