Preparation of lactose‐free milk by using salt‐fractionated almond (Amygdalus communis) β‐galactosidase

β‐galactosidase was isolated from almond (Amygdalus communis) extract by ammonium sulfate precipitation. Almond proteins precipitated by using ammonium sulfate and then dialysed exhibited 5.3‐fold purification of β‐galactosidase, and the yield of enzyme preparation was 96.5%. The partially purified β‐galactosidase exhibited pH and temperature optima at pH 5.5 and 50 °C, respectively. The enzyme was significantly stable against heat, pH, calcium and magnesium ions and D ‐galactose. The almond β‐galactosidase preparation exhibited over 89% activity even after 2 months storage at 4 °C. Hydrolysis of lactose in milk and whey was performed in a stirred batch process by using this enzyme preparation. These observations indicated that the hydrolysis of lactose increased continuously with time. The enzyme could hydrolyse 94% of lactose in buffer solution and whey whereas 90% of lactose hydrolysis was achieved in milk. The main aim of the present study was to prepare lactose‐free milk, which must be free from contamination, and the process should be inexpensive. Copyright © 2007 Society of Chemical Industry     

Electrophoretic patterns of microwaved and γ‐irradiated beef liver proteins

The effects of γ‐irradiation treatments (2.5, 5 and 10 kGy) and microwaves generated from an oven at low and defrost power settings for 0.5, 1 and 2 min on the total proteins and protein patterns of beef liver immediately after treatment and during frozen storage (?18 °C) for different periods were studied. Chemical analyses indicated that the protein content of beef liver was reduced after exposure to γ‐radiation or microwaves and also during frozen storage. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS‐PAGE) was used to illustrate the changes in protein bands of different molecular weights and their percentages before and after exposure to gamma and microwave radiation. The main effect of γ‐radiation on the protein patterns of beef liver was the disappearance of some high‐molecular‐weight protein bands and the development of other bands characterised by moderate and low molecular weights. This finding indicates the degradation of beef liver proteins by γ‐irradiation. In contrast, microwave treatment caused an increase in the levels of high‐molecular‐weight protein bands with a concomitant decrease in low‐molecular‐weight protein bands. This phenomenon demonstrates the polymerisation of low‐molecular‐weight proteins under the influence of microwaves. © 2001 Society of Chemical Industry     

Influence of Maillard reaction conditions on the antigenicity of bovine α‐lactalbumin using response surface methodology

BACKGROUND: Maillard reaction can modify functional properties of proteins. Bovine α‐lactalbumin (α‐LA) is often supplemented to the new generation of infant formulae, but it is considered to be a main allergen. However, there is little information on the effect of Maillard reaction on α‐LA antigenicity. The objective of this study was to investigate the influence of Maillard reaction on the antigenicity of α‐LA in conjugates of whey protein isolate (WPI) with glucose under different conditions of protein/sugar weight ratio (0.17–7.83), temperature (40–60 °C) and time (24–120 h) using response surface methodology. RESULTS: Conjugation of WPI with glucose markedly reduced the antigenicity of α‐LA. This reduction in antigenicity could be controlled by regulating the three independent variables weight ratio, temperature and time. A model of optimal reaction conditions for lower antigenicity of α‐LA was established. According to the model, the minimum antigenicity of α‐LA was achieved at 52.8 °C, 78 h and 5.96:1 WPI/glucose weight ratio. WPI/glucose weight ratio had the greatest effect on the antigenicity of α‐LA, while reaction temperature influenced α‐LA antigenicity to a lesser extent. CONCLUSION: Well‐controlled Maillard reaction between WPI and glucose is an efficient method to reduce α‐LA antigencity. Copyright © 2009 Society of Chemical Industry     

Shelf‐life extension of vacuum‐packaged sea bream (Sparus aurata) fillets by combined γ‐irradiation and refrigeration: microbiological,chemical and sensory changes

The combined effect of γ‐irradiation and refrigeration on the shelf‐life of vacuum‐packaged sea bream (Sparus aurata) fillets was studied by monitoring the microbiological, chemical and sensory changes of non‐irradiated and irradiated fish samples using low‐dose irradiation doses of 1 and 3 kGy. Fish species such as sea bream and sea bass are very popular in the Mediterranean countries due to their high quality characteristics, and their preservation is a constant challenge given their extreme perishability. Irradiation (3 kGy) dramatically reduced populations of bacteria, namely, total viable counts (3 vs 7 log cfu g^?1) for the non‐irradiated samples, Pseudomonas spp (<2 vs 7.6 log cfu g^?1), H₂S‐producing bacteria typical of Shewanella putrefaciens (<2 vs 5.9 log cfu g^?1), Enterobacteriaceae (<2 vs 6.0 log cfu g^?1) and lactic acid bacteria (<2 vs 3.5 log cfu g^?1) after 10 days of storage. The effect was more pronounced at the higher dose (3 kGy). Lactic acid bacteria, Enterobacteriaceae and H₂S‐producing bacteria typical of Shewanella putrefaciens showed higher sensitivity to γ‐radiation than did the rest of the microbial species. Of the chemical indicators of spoilage, Trimethylamine (TMA) values of non‐irradiated sea bream increased very slowly, whereas for irradiated samples significantly lower values were obtained reaching a final value of 7.9 and 6.3 mg N per 100 g muscle at 1 and 3 kGy respectively (day 42). Total volatile basic nitrogen (TVB‐N) values increased slowly attaining a value of 67.3 mg N per 100 g for non‐irradiated sea bream during refrigerated storage, whereas for irradiated fish, lower values of 52.8 and 43.1 mg N per 100 g muscle were recorded (day 42). Thiobarbituric acid (TBA) values for irradiated sea bream samples were higher than respective non‐irradiated fish and increased slowly until day 21 of storage, reaching final values of 1.1 (non‐irradiated), 2.0 (1 kGy) and 2.2 mg malonaldehyde kg^?1 muscle (3 kGy), respectively (day 42). Sensory evaluation showed a good correlation with bacterial populations. On the basis of overall acceptability scores (sensory evaluation) a shelf‐life of 28 days (3 kGy) was obtained for vacuum‐packaged sea bream, compared with a shelf‐life of 9–10 days for the non‐irradiated sample. Copyright © 2004 Society of Chemical Industry     

Effect of γ‐irradiation on post‐harvest ripening of plantain fruit (Musa paradisiaca) cultivars

Three plantain cultivars, Agbagba, Obino L'ewai and Cardaba, harvested at two stages of maturity, were irradiated at 0.1–1.0 kGy prior to storage under tropical ambient conditions. Post‐irradiation storage behaviour showed that plantain fruits at full three‐quarter grade were more responsive to irradiation treatment than at full grade maturity, while Cardaba, a type of cooking banana, showed the least response. Irrespective of varietal differences, irradiation to 0.5 kGy or higher caused severe tissue damage, softening and skin discolouration; however, γ‐irradiation at optimum dose range of 0.15–0.30 kGy effectively delayed ripening for 10–12 days in Agbagba and Obino L'ewai, respectively, without affecting respiratory pattern or fruit quality. © 1999 Society of Chemical Industry     

Reduction in flatulence factors in mung beans (Vigna radiata) using low‐dose γ‐irradiation

Mungbeans (Vigna radiata), control and γ‐irradiated at insect disinfestation dose levels (0.25 and 0.75 kGy) were germinated (0–6 days) and the qualitative and quantitative changes in soluble carbohydrates were studied in detail. The key flatulence‐producing raffinose family oligosaccharides in mungbeans were degraded in the irradiated samples at the onset of the germination (0–2 days) compared to the control where it occurred much later (>4 days). However, the reducing sugars, mainly glucose, fructose and galactose, which are metabolised easily, were enhanced in the irradiated samples. At low dose (0.25 kGy), irradiation had no effect on germination and sprout length, indicating that irradiated beans are suitable for use as sprouted beans. These observations clearly indicate that γ‐irradiation at insect disinfestation dose levels improved the digestibility and nutritional quality of mung beans by reducing the content of oligosaccharides responsible for intestinal gas production. © 1999 Society of Chemical Industry     

Interaction of β‐casein with (−)‐epigallocatechin‐3‐gallate assayed by fluorescence quenching: effect of thermal processing temperature

The interactions between the flavan‐3‐ol (?)‐epigallocatechin‐3‐gallate (EGCG) and bovine β‐casein in phosphate‐buffered saline (PBS) of pH 6.5 subjected to thermal processing at various temperatures (25–100 °C) were investigated using fluorescence quenching. The results indicated that different temperatures had different effects on the structural changes and EGCG‐binding ability of β‐casein. At temperatures below 60 °C, the β‐casein–EGCG interaction changed little (P > 0.05) with increasing temperature. At temperatures above 80 °C, native assemblies of β‐casein in solution dissociated into individual β‐casein molecules and unfolded, as demonstrated by a red shift of the maximum fluorescence emission wavelength (λ_max) of up to 8.8 nm. The highest quenching constant (K_q) and the number of binding sites (n) were 0.92 (±0.01) × 10¹³ m ^?1 s^?1 and 0.73 (±0.02) (100 °C), respectively. These results provide insight into the potential of interactions between β‐casein–EGCG that may modulate bioactivity or bioavailability to be altered during thermal process.     

Purification and physicochemical characterization of ovine β‐lactoglobulin and α‐lactalbumin

Ovine whey proteins were fractionated and studied by using different analytical techniques. Anion‐exchange chromatography and reversed‐phase high‐performance liquid chromatography (HPLC) showed the presence of two fractions of β‐lactoglobulin but only one of α‐lactalbumin. Gel permeation and sodium dodecyl sulfate (SDS)‐polyacrylamide gel electrophoresis allowed the calculation of the apparent molecular mass of each component, while HPLC coupled to electrospray ionisation‐mass spectrometry (ESI‐MS) technique, giving the exact molecular masses, demonstrated the presence of two variants A and B of ovine β‐lactoglobulin. Amino acid compositions of the two variants of β‐lactoglobulin differed only in their His and Tyr contents. Circular dichroism spectroscopy profiles showed pH conformation changes of each component. The thermograms of the different whey protein components showed a higher heat resistance of β‐lactoglobulin A compared to β‐lactoglobulin B at pH 2, and indicated high instability of ovine α‐lactalbumin at this pH.     

Screening of β‐Glucosidase and β‐Xylosidase Activities in Four Non‐Saccharomyces Yeast Isolates

The finding of new isolates of non‐Saccharomyces yeasts, showing beneficial enzymes (such as β‐glucosidase and β‐xylosidase), can contribute to the production of quality wines. In a selection and characterization program, we have studied 114 isolates of non‐Saccharomyces yeasts. Four isolates were selected because of their both high β‐glucosidase and β‐xylosidase activities. The ribosomal D1/D2 regions were sequenced to identify them as Pichia membranifaciens Pm7, Hanseniaspora vineae Hv3, H. uvarum Hu8, and Wickerhamomyces anomalus Wa1. The induction process was optimized to be carried on YNB‐medium supplemented with 4% xylan, inoculated with 106 cfu/mL and incubated 48 h at 28 °C without agitation. Most of the strains had a pH optimum of 5.0 to 6.0 for both the β‐glucosidase and β‐xylosidase activities. The effect of sugars was different for each isolate and activity. Each isolate showed a characteristic set of inhibition, enhancement or null effect for β‐glucosidase and β‐xylosidase. The volatile compounds liberated from wine incubated with each of the 4 yeasts were also studied, showing an overall terpene increase (1.1 to 1.3‐folds) when wines were treated with non‐Saccharomyces isolates. In detail, terpineol, 4‐vinyl‐phenol and 2‐methoxy‐4‐vinylphenol increased after the addition of Hanseniaspora isolates. Wines treated with Hanseniaspora, Wickerhamomyces, or Pichia produced more 2‐phenyl ethanol than those inoculated with other yeasts.     

Effect of γ‐irradiation on the biophysical and morphological properties of corn

The effects of γ‐irradiation on the biophysical and morphological properties of corn plants were investigated. The irradiation doses were 0, 1, 1.5, 2.5, 5, and 10 krad. Corn grains exposed to 1.5 and 2.5 krad showed highly significant changes in all growth parameters. Fluorescence and light absorption spectra of chlorophyll attributed to different doses treatments of corn grains clearly confirmed the superiority of 1.5 krad irradiation dose in stimulating corn plants. Furthermore, the frequency dependence of the relative permittivity and the electric conductivity of the treated samples have been performed and discussed. The obtained results give another support via the biophysical properties for the 1.5 krad irradiation dose to be the most favorable one to improve the plant growth characteristics.     

Physical,proximate, functional and pasting properties of four non‐ and γ‐irradiated bambara groundnut (Vigna subterranean) cultivars

Effect of γ‐irradiation (2–30 kGy) on physical, proximate, functional and pasting properties of four bambara groundnut cultivars was investigated. Packed (0.74–0.75 g mL^?1) and loose (0.71–0.76 g mL^?1) density varied significantly among cultivars. Generally, CIE L and hue angle decreased, while CIE a, b, deltachroma and colour intensity increased with increased dose. Protein (21.23–23.77 g/100 g), fat (6.38–7.69 g/100 g), crude fibre (1.28–3.54 g/100 g), ash (1.50–4.50 g/100 g) and moisture (10.67–12.92 g/100 g) of non‐ and γ‐irradiated bambara varied with cultivars and dose. Loose (0.41–0.49 g mL^?1) and packed (0.54–0.74 g mL^?1) densities, water absorption (1.62–2.38 g/g) and swelling (10.50–18.00 g/g) increased marginally, while oil absorption (1.93–2.82 g/g), alkaline water retention (0.66–1.23 g/g), emulsion capacity (40.31–58.23%) and stability (31.67–46.49%) decreased with increased dose. Foam capacity (6.85–22.37%) and stability (1.80–22.37%) of γ‐irradiated flours were higher than their nonirradiated (2.03–18.26%) counterparts. Nonirradiated flours showed significantly higher viscosities than their γ‐irradiated counterparts. Flours showed slightly shear‐thinning behaviours.     

Inhibitory activities of kaempferol,galangin, carnosic acid and polydatin against glycation and α‐amylase and α‐glucosidase enzymes

The activities of four natural phenolics, kaempferol, galangin, carnosic acid and polydatin in scavenging free radicals, inhibiting advanced glycation end‐product (AGE) formation, α‐amylase and α‐glucosidase and trapping methylglyoxal (MGO), were evaluated in this study. Carnosic acid and galangin had the highest activity in scavenging free radicals. Kaempferol and galangin had the greatest activity in preventing bovine serum albumin (BSA) against glycation and reducing glycated proteins. Polydatin had the greatest performance in trapping MGO to reduce glycation reaction. However, there was no significant difference for kaempferol, galangin and carnosic acid in inhibiting AGE formation by BSA‐MGO reaction. Kaempferol, galangin and carnosic acid were the competitive inhibitors for α‐amylase, while kaempferol and carnosic acid were noncompetitive inhibitors for α‐glucosidase. However, polydatin showed as a mixed noncompetitive inhibitor for both α‐amylase and α‐glucosidase. The results indicated that the four natural phenolics have potential in inhibiting AGE production and the digestive enzymatic activity with different mechanisms.     

Enhanced bioaccessibility of β‐carotene from yellow‐orange vegetables and green leafy vegetables by domestic heat processing

Effect of heat treatment involved in domestic cooking on the bioaccessibility of β‐carotene from yellow‐orange as well as green leafy vegetables was evaluated. Heat treatment of these vegetables by pressure‐cooking, stir‐frying and open‐pan boiling had a beneficial influence on the bioaccessibility of β‐carotene. The extent of increase in the per cent bioaccessibility of β‐carotene as a result of pressure‐cooking was 21–84%. Stir‐frying in presence of a small quantity of oil brought about an enormous increase in the bioaccessibility of β‐carotene from these vegetables, the extent of increase being 67–191%. Open‐pan boiling of vegetables increased the bioaccessibility of β‐carotene in the range 23–36%. Thus, among the three domestic heat processing methods, stir‐frying results in maximum bioaccessibility of this provitamin. The use of suitably heat‐processed vegetable sources of β‐carotene could form a dietary strategy to derive this micronutrient maximally by the population dependent on plant foods.     

Effects of the β‐glycosidase reaction on bio‐conversion of isoflavones and quality during tofu processing

BACKGROUND: Isoflavones are the most common group of phytoestrogens which are present in significantly large amounts in soybean and soy products such as tofu. Isoflavones occur naturally in glycoside forms having lower bioavailability than their aglycone forms. β‐Glycosidase acts as a bio‐catalyst for the conversion of isoflavone glycosides to isoflavone aglycones, raising the bioavailability of isoflavones; therefore, it can be used to improve the quality of tofu. We need to establish process conditions for the optimal outcome of the enzyme reaction in tofu. RESULTS: By using the β‐glycosidase (0.02% w/v) reaction at 55 °C for 30 min, a maximum 84.5% conversion of isoflavone glycoside to isoflavone aglycone was obtained. The enzyme reaction caused no significant effects on the sensory acceptability of soft tofu. The hardness of enzyme‐treated hard tofu increased with the coagulant amount whereas prolonged heating resulted in decrease of hardness. Incorporation of enzyme reaction before the coagulation process during soft tofu processing provided a sufficient bio‐conversion of isoflavones at optimal conditions. CONCLUSION: β‐Glycosidase can be effectively used for the bioconversion of isoflavones in soft tofu manufacturing process at optimal reaction conditions before the onset of coagulation process. Copyright © 2010 Society of Chemical Industry     

Characterization of the Supermolecular Structure of Polydatin/6‐O‐α‐Maltosyl‐β‐cyclodextrin Inclusion Complex

Polydatin is the main bioactive ingredient in many medicinal plants, such as Hu‐zhang (Polygonum cuspidatum), with many bioactivities. However, its poor aqueous solubility restricts its application in functional food. In this work, 6‐O‐α‐Maltosyl‐β‐cyclodextrin (Malt‐β‐CD), a new kind of β‐CD derivative was used to enhance the aqueous solubility and stability of polydatin by forming the inclusion complex. The phase solubility study showed that polydatin and Malt‐β‐CD could form the complex with the stoichiometric ratio of 1:1. The supermolecular structure of the polydatin/Malt‐β‐CD complex was characterized by ultraviolet–visible spectroscopy (UV), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffractometry (XRD), thermogravimetric/differential scanning calorimetry (TG/DSC), and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy. The changes of the characteristic spectral and thermal properties of polydatin suggested that polydatin could entrap inside the cavity of Malt‐β‐CD. Furthermore, to reasonably understand the complexation mode, the supermolecular structure of polydatin/Malt‐β‐CD inclusion complex was postulated by a molecular docking method based on Autodock 4.2.3. It was clearly observed that the ring B of polydatin oriented toward the narrow rim of Malt‐β‐CD with ring A and glucosyl group practically exposed to the wide rim by hydrogen bonding, which was in a good agreement with the spectral data.     

Modification of poovan banana (Musa AAB) starch by γ‐irradiation: effect on in vitro digestibility,molecular structure and physico‐chemical properties

This study focussed at evaluating the effect of gamma irradiation on the in vitro digestibility, molecular structure and physico‐chemical properties of poovan banana (Musa AAB) starch using γ‐rays from a ⁶⁰Co source at different doses with a dose rate of 2 kGy h^?1. Physico‐chemical properties varied significantly and exhibited strong dose‐dependent relationship. Escalating irradiation leads to decrease in amylose content, pH, swelling power of the starch granules and syneresis of the gelatinised starch, while the same led to an increase in carboxyl content, in vitro digestibility, solubility and water absorption capacity of the starch granules. The results revealed that peak, hold, final and setback viscosities were significantly reduced. X‐ray diffraction pattern remained the same upon irradiation but a decrease in relative crystallinity was observed with increasing irradiation dose. Gelatinisation temperature and enthalpy decreased significantly when the increasing the dose of gamma irradiation.