Debittering of Tangerine Citrus Reticulata Blanco Juice by β-Cyclodextrin Polymer

Preparation of limonin monoclonal antibody and establishment of a sensitive icELISA for analyzing limonin in citrus and herbal samples

Limonin is an intensely bitter and highly oxidized tetracyclic triterpenoid secondary metabolite, which is abundant in the Rutaceae and Meliaceae, especially in Citrus. In order to detect limonin content in complex substrates such as citrus and traditional Chinese medicine, monoclonal antibodies specifically recognizing limonin were prepared and an indirect competitive enzyme-linked immunosorbent assay (icELISA) was established. The median inhibition concentration (IC50) was 5.40 ng/mL and the linear range was 1.25-23.84 ng/mL. The average recoveries from citrus peel and pulp samples were 95.9%-118.8% and 77.5%-113.1%, respectively. Moreover, the contents of limonin in 6 citrus samples and 4 herbal samples were analyzed by icELISA and UPLC-MS, and the results of the two methods were consistent. This validation is sufficient to demonstrate that the developed immunoassay is applicable for the detection of limonin in citrus and herbal samples and has the advantage of high efficiency, sensitivity, and convenience.

One pot clarification and debittering of grapefruit juice using co-immobilized enzymes@chitosanMNPs

In the present work, enzymes pectinase and naringinase were simultaneously co-immobilized on an eco-friendly chitosan coated magnetic nanoparticles (chitosanMNPs) by cross-linking using chitosan as a macro-molecular cross-linker. The maximum activity recovery of both enzymes in the co-immobilized form was obtained at chitosanMNPs to enzymes ratio of 1:3, 3% cross-linker concentration and 150 min cross-linking time. The synthesized MNPs before and after co-immobilization were characterized using different techniques. The prepared biocatalyst was found spherical with an average size below 200 nm and showed supermagnetic property with saturation magnetization of 38.28 emu/g. The optimum pH and temperature of both enzymes in co-immobilized form was found at 5.5 and 65 °C. The prepared biocatalyst exhibited an improved thermal stability with 1.8-fold increase in the half-life. The secondary structural analysis revealed that, prepared co-immobilized biocatalyst undergone changes in the conformational and structural rigidity due to macro-molecular cross-linker. The co-immobilized biocatalysts were evaluated for one pot clarification and debittering of grapefruit juice and found ~52% reduction in turbidity and ~85% reduction in the naringin content. The co-immobilized enzymes were recycled up to 7^th cycle and can be easily stored at room temperature for 30 days retaining up to 64% and 86% residual activities respectively.

Changes in bitterness, antioxidant activity and total phenolic content of grapefruit juice fermented by Lactobacillus and Bifidobacterium strains

Four strains of Lactobacillus and Bifidobacterium including L. plantarum 01, L. fermentum D13, L. rhamnosus B01725, and B. bifidum B7.5 exhibiting naringinase production were applied in grapefruit juice fermentation. All investigated strains grew well in grapefruit juice without nutrition supplementation. In all cases, cell counts were 108–109 CFU ml−1 after 24 hours of fermentation. The highest lactic acid and acetic acid productions were observed in the case of strain L. plantarum 01. The L. plantarum 01 and L. fermentum D13 strains prefer glucose over fructose and sucrose, whereas fructose was the most favoured sugar for L. rhamnosus B01725 and B. bifidum B7.5. At the end of the fermentation process, antioxidant activity and total polyphenol content of grapefruit juice decreased in all cases, but the changes were not significant. Significant decrease of naringin was observed in the case of L. plantarum 01, 28% naringin in grapefruit juice was removed after fermentation. This result is promising for development of technology for production of probiotic grapefruit juice.

Immobilization of Naringinase from Penicillium decumbens on Chitosan Microspheres for Debittering Grapefruit Juice

Naringinase is an enzyme complex which exhibits α-l-rhamnosidase and β-d-glucosidase activity. This enzymatic complex catalyzes the hydrolysis of naringin (4',5,7-trihydroxy flavanone 7-rhamnoglucoside), the main bittering component in grapefruit. Reduction of the level of this substance during the processing of juice has been the focus of many studies. The aim of the study was the immobilization of naringinase on chitosan microspheres activated with glutaraldehyde and, finally, the use of such immobilized enzyme for debittering grapefruit juice. The effect of naringinase concentration and characterization of the immobilized enzyme compared to the soluble enzyme were investigated. The maximum activity was observed at optimum pH 4.0 for both free and immobilized naringinase. However, the optimum temperature was shifted from 70 to 40 °C upon immobilization. The KM value of the immobilized naringinase was higher than that of soluble naringinase. The immobilization did not change the thermal stability of the enzyme. The immobilized naringinase had good operational stability. This preparation retained 88.1 ± 2.8% of its initial activity after ten runs of naringin hydrolysis from fresh grapefruit juice. The results indicate that naringinase immobilized on chitosan has potential applicability for debittering and improving the sensory properties of grapefruit juices.

Effects of Postharvest Time, Heat Treatment, pH and Filtration on the Limonin Content in Newhall Navel Orange (Citrus sinensis Osbeck cv. Newhall) Juice

Delayed bitterness causes severe economic loss in citrus juice industry worldwide, which is mostly due to the formation of limonoid compounds, especially limonin, in juice. In this study, effects of postharvest time of fruits, heat treatment, pH and filtration of juice on limonin content in Newhall navel orange (Citrus sinensis Osbeck cv. Newhall) juice were investigated. Our research indicated for the first time that: (1) limonin content in juice would gradually increase to a maximal level and then remained almost constant thereafter as storage time going on, whereas the maximum constant value (MCV) of limonin content in juice significantly (p < 0.05) decreased with the increment of postharvest time of fruits being juiced; (2) heat treatment and acidification of juice only speeded up the formation of limonin to the maximal level while without changing the MCV of limonin content; (3) the juice after filtration exhibited much lower MCV of limonin content compared with the unfiltered one. These experimental observations might not only provide useful information for the development of new debitterness method for navel orange juice, but also strongly support the acid-promoted delayed bitterness mechanism, suggesting the formation of delayed bitterness might primary due to the acid-promoted rather than the enzyme-catalyzed lactonization of limonoate A-ring lactone (LARL) to produce limonin in juice of navel orange.

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.

Efficacy of various techniques on biochemical characteristics and bitterness of pummelo juice

The consumer acceptability of pummelo juice is affected badly due to the presence of bitter principles in it. Therefore in order to avoid such bitterness development, the extracted juice from pummelo was subjected to five different treatments like juice diffused into syrup (70°Brix), lye peeling of segments in boiling NaOH for 2-3 min, increasing the pH of juice, hot water treatment (50 °C) prior to peeling for 20 min and without any treatment (control) for suppressing the development of bitterness in the juice. Based on bio-chemical analysis, diffusion of juice into syrup (70°Brix) showed better result as compared to other treatments. The maximum amount of TSS was found in juice diffused into syrup (i. e. 45, 30 and 15°Brix) along with highest TSS/acid ratio (92.21, 49.87 and 17.53). Higher amount of acidity was observed in pH adjusted samples with 4.25, 4.50 and 4.75 respectively. However, control samples showed higher amount of ascorbic acid (73.97 mg/100 ml juice) content followed by pH adjusted samples. The highest organoleptic score for taste (8.00), colour (8.83), aroma (8.66), overall acceptability (7.88) and extent of debittering (7.50) were recorded in juice diffused into syrup 70°Brix and achieved final TSS of juice at 45, 30 and 15°Brix respectively. Moreover, the above treatment (juice diffused into syrup 70°Brix) showed promising low cost and easy to adopt technique of debittering in respect of extent of debittering and maintaining sensory quality during storage of pummel juice.