Production and characterisation of antioxidant peptides from sweet potato protein by enzymatic hydrolysis with radio frequency pretreatment

Effect of radio frequency (RF at 70, 80 and 90 °C) pretreatment on production and characterisation of sweet potato protein hydrolysates (SPPH) prepared using Alcalase (ALC), Protease (PRO) and the combination of ALC + PRO was investigated. RF highly improved degree of hydrolysis (DH) and enhanced antioxidant activity of all SPPH produced by ALC, PRO and the combination as compared to traditional water bath (WB) heating pretreatment (P < 0.05). RF significantly increased molecular weight (MW) <3 kDa peptide fraction from SPPH produced by ALC, and MW <3 kDa peptide fraction from RF80- and RF90-pretreated samples has higher antioxidant activity. Diverse peptides in MW <3 kDa fractions with RF80 and RF90 pretreatments were identified using LC–QTOF–MS/MS, which matched the sequences of sporamins and contained antioxidant amino acids Trp, Tyr, Met, Phe and/or His. There is a great potential application of using SPPH in functional foods as a novel ingredient.     

Preparation and identification of angiotensin I-converting enzyme inhibitory peptides from sweet potato protein by enzymatic hydrolysis under high hydrostatic pressure

Sweet potato protein hydrolysates (SPPH) with angiotensin I-converting enzyme (ACE) inhibitory activity were prepared by papain, pepsin and alcalase under high hydrostatic pressure (HHP, 100–300 MPa). HHP significantly increased degree of hydrolysis (DH), nitrogen recovery (NR) and molecular weight (MW) <3 kDa fractions contents of SPPH by all three enzymes (P < 0.05). MW < 3 kDa peptide fractions from SPPH by alcalase under 100 MPa showed the highest ACE inhibitory activity (IC₅₀ value 32.24 µg mL⁻¹), and was subjected to purification and identification by semi-preparative RP-HPLC and LC-MS/MS. Fifty-four peptides ranged from 501.28 to 1958.88 Da with 5–18 amino acids were identified and matched sporamin A and B sequences. Five identified peptides with sequences of VSAIW, AIWGA, FVIKP, VVMPSTF and FHDPMLR displayed good ACE inhibitory activity with the contribution of Val, Trp, Phe and Arg. Thus, SPPH by enzymatic hydrolysis under HHP can be potentially used in functional food.     

Contribution of different molecular weight fractions to anticancer effect of sweet potato protein hydrolysates by six proteases on HT‐29 colon cancer cells

The contribution of different molecular weight fractions to anticancer effect of sweet potato protein hydrolysates (SPPH) by six proteases on HT‐29 colon cancer cells was investigated. SPPH prepared by six proteases showed certain antiproliferation effect on HT‐29 cells. Compared with other five proteases, SPPH by Alcalase exhibited the highest antiproliferation effect with the lowest IC₅₀ value of 119.72 μg mL^?1. SPPH by Alcalase was further separated into four fractions (>10, 5–10, 3–5 and <3 kDa), and <3 kDa fractions showed the strongest antiproliferation effect, which was 43.87% at 100 μg mL^?1 (P < 0.05). The <3 kDa fractions could cause G2/M cell cycle arrest with increased p21 expression and induce apoptosis via decreasing Bcl‐2 expression, increasing Bax expression and inducing caspase‐3 activation in HT‐29 cells. In addition, <3 kDa fractions could significantly inhibit cell migration of HT‐29 cells. Thus, SPPH might be potentially used as a natural supplement in functional foods.     

Identification and characterization of antioxidant peptides from sweet potato protein hydrolysates by Alcalase under high hydrostatic pressure

Sweet potato protein hydrolysates (SPPH) were generated by Alcalase under high hydrostatic pressure (HHP, 100, 200 and 300 MPa). HHP significantly improved the degree of hydrolysis (DH) and antioxidant activity, and increased the < 3 kDa fraction content of SPPH (P < 0.05). SPPH by Alcalase at 300 MPa for 60 min exhibited the highest DH and antioxidant activity and was separated into three fractions by ultrafiltration. The most active fraction FIII (< 3 kDa) was further separated into fifty four fractions by semi-preparative RP-HPLC and measured using the ORAC assay. In addition, more active fractions were examined by LC–MS/MS, and diverse peptides were identified, matching sequences of Sporamins A and B. To evaluate the structure–activity dependences, twenty sequences were synthesized, of which the antioxidant activity was assessed. Five peptides showed good activity: HDSASGQY ≥ YYMVSA ≥ HDSESGQY ~ YYIVS ~ RYYDPL, with the contribution of His and Tyr.Industrial relevanceThis study will give a novel technique for using industrial waste slurry, a byproduct in the process of sweet potato starch manufacturing, which contains various bioactive components (such as protein, minerals, etc.) since most of them are normally discarded. The present study is focused on assessing the effects of enzymatic hydrolysis by Alcalase under high hydrostatic pressure (HHP) on the release of antioxidant peptides from sweet potato protein (SPP). The results of this work provide a potential application of enzymatic hydrolysis assisted by HHP on the development of ingredients from SPP in functional foods.     

Antioxidant activities of Rapana venosa meat and visceral mass during simulated gastrointestinal digestion and their membrane ultrafiltration fractions

Rapana venosa (Rv) is an abundant marine snail resource with high content of protein. The antioxidant activities of Rv meat and visceral mass during simulated gastrointestinal (GI) digestion and their membrane ultrafiltration fractions were evaluated. Results indicated that visceral mass possessed stronger antioxidant activities than meat. The simulated GI digestion increased the hydroxyl radical scavenging activity while decreased the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) scavenging activity and reducing power. After membrane ultrafiltration, there were three fractions, that is molecular weight (MW) > 10 kDa, MW 3.5–10 kDa and MW < 3.5 kDa. Fractions with MW > 10 kDa and MW < 3.5 kDa showed the highest hydroxyl, DPPH radical scavenging activity, respectively. Fractions with MW 3.5–10 kDa and MW > 10 kDa showed the highest reducing power for meat and visceral mass, respectively. Rv hydrolysates exhibited significantly higher hydroxyl radical scavenging activity than the positive control vitamin C (Vc) and may serve as useful ingredients for application in food industry nutritional products.     

Biochemical and antioxidant properties of peptidic fraction generated from crab (Portunus trituberculatus) shells by enzymatic hydrolysis

The biochemical properties and in vitro antioxidant activity of the crab (Portunus trituberculatus) shell hydrolysates (CSHs) generated by pepsin and protamex hydrolysis were evaluated. The amino acids profile of CSHs showed a high percentage of essential amino acids (>36%). The hydrolysates were mainly composed of low molecular weight peptides (<3 kDa). CSHs showed excellent solubility and possessed interfacial properties, which were governed by their concentrations. The antioxidant activities of CSHs were evaluated using various in vitro antioxidant assays, including the total antioxidant activity, DPPH, hydroxyl and ABTS radical scavenging method and reducing power assay. CSHs exhibited a good antioxidant activity compared to that of ascorbic acid. Results from this study suggested that the peptidic fractions of crab shells were good source of natural antioxidants and peptides with interesting functionalities.     

Identification of active peptides from backbones of Nemipterus japonicus and Exocoetus volitans by electrospray ionisation–mass spectrometry

In our present investigation, Nemipterus japonicus and Exocoetus volitans backbone protein were hydrolysed by proteases like trypsin and pepsin, respectively. The protein hydrolysates were purified by different chromatographic methods, and the resulted purified peptides were analysed for their amino acid sequences by electrospray ionisation–MS/MS. The analysis of peptides showed sequences as Gly‐His‐Met‐Ser (451.8 Da) and Leu‐Glu‐Val‐Lys‐Pro (596.9 Da) for N. japonicus and E. volitans muscle, respectively. The presence of hydrophobic amino acids contributes more to the antioxidant activities of peptides than other amino acids. Moreover, sequence of amino acids in peptides plays an important role in their antioxidant activities.     

Effects of thermal processing on antioxidant activities,amino acid composition and protein molecular weight distributions of jasmine rice bran protein hydrolysate

This research aimed to evaluate the effects of thermal processing on the amino acid composition, molecular weight distribution (MW) and antioxidant activities of Jasmine rice bran protein hydrolysates (JBH). JBH was prepared by enzymatic hydrolysate (alcalase and flavourzyme at a ratio of 9.81:90.19, 2.84% w/w) for 60 min. JBH samples were treated as follows: non-heat (NJBH), pasteurisation (72ºC, 15 min; PJBH) and sterilisation (121ºC, 15 min; SJBH). For SJBH treatment, the browning index and fluorescence intensity increased (P < 0.05). FTIR showed that thermal process changed the intensities and location of some bands. Thermal processing affected MW by decreasing it from high MW (>10 kDa) to medium (3–10 kDa) and low MW (<3 kDa). Val, Met, Ile and Leu contents increased after thermal processing. Compared with NJBH, the IC₅₀ values of ABTS and FRAP of SJBH were not significantly different, while the IC₅₀ of DPPH increased (P ≥ 0.05).     

Osteoarthritis-alleviating effects in papain-induced model rats of chicken cartilage hydrolysate and its peptide fractions

This study aims to discover natural bioactive substances as alternative therapies to current medical and surgical treatments for osteoarthritis (OA). Chicken cartilage hydrolysate (CCH) was produced using trypsin and separated via ultrafiltration into CCH-I (molecular weight (MW) > 10 kDa) and CCH-II (MW <10 kDa). Results showed that CCH and its fractions (CCH-I and CCH-II) could relieve OA with different extents, and the outcome using these treatments depended on their especial composition. CCH-II (a fraction rich in low MW peptides with no chondroitin sulphate (CS) and low in sugar) exhibited desired OA-alleviating effect in papain-induced rat and highest in vitro antioxidant activities. CCH-I (a fraction rich in CS and in high MW peptides) might have an adverse effect on renal function. Therefore, it is industrially feasible to produce anti-inflammatory and antioxidative CCH, especially CCH-II, with the therapeutic potential for alleviating or treating OA. Further separation of CS from CCH-I may lead to a commercial pure CS product for treating OA.     

Bioactive peptides from collagen hydrolysates from squid (Dosidicus gigas) by-products fractionated by ultrafiltration

The bioactive properties of peptide fractions obtained from the hydrolysis of squid (Dosidicus gigas) by-products collagen, using Protease type XIV and ultrafiltration (UFI), were studied. The basic objective was to improve the bioactivity of squid hydrolysates via the application of UFI. Peptide fractions obtained after UFI had higher antioxidant and antimutagenic activities, but the antiproliferative activity did not improve after UFI. Peptides <5 kDa (Fraction F3) showed higher antioxidant and antimutagenic activities, as well as lower antioxidant and antiproliferative activities than both, peptides >10 kDa (F1) and those within the range of >5 to <10 kDa (F2). Band at lower field observed in FT-IR spectra and proton-peaks observed at higher ¹H-NMR fields, both associated to aromatic amino acids, as well as to other antioxidant amino acids such as hydroxyproline, glycine, arginine and lysine, may explain F3 bioactivity. Ultrafiltration can, therefore, be used to improve some bioactivities of squid collagen hydrolysates.     

Fractionation and purification of antioxidant peptides from abalone viscera by a combination of Sephadex G-15 and Toyopearl HW-40F chromatography

Abalone viscera, a protein-rich by-products from the abalone processing industry, are normally discarded as wastes. In the present study, four different proteases were used to hydrolyse abalone viscera to prepare high-activity antioxidant peptides, and their hydrolysis effects were compared. Although the hydrolytic abilities of papain and trypsin were inferior to the alcalase and neutrase, their use resulted in significantly (P < 0.05) higher scavenging activities for DPPH. The hydrolysates mainly consisted of peptides with a molecular weight <3 kDa, and the fractionation was achieved using a combination of Sephadex G-15 and Toyopearl HW-40F gel filtration chromatography, which overcomes the disadvantages of traditional membrane separation technology in fractionating peptides with relatively similar molecular weight distribution. The DPPH scavenging activities of the components containing peptides <1 kDa (fractions E) were significantly (P < 0.01) higher than those containing peptides >1 kDa. The different fractions E were further purified by reversed-phase high-performance liquid chromatography, and a total of 16 target peptides, containing 4-8 amino acids, enriched in hydrophobic amino acids and C-terminal Arg, with molecular weights ranging from 500 to 850 Da, were identified.     

Optimisation of antioxidant hydrolysate production from sweet potato protein and effect of in vitro gastrointestinal digestion

In this study, response surface methodology (RSM) was applied to optimise antioxidant hydrolysate production from sweet potato protein (SPP). The effects of enzyme‐to‐substrate ratio, pH value and reaction temperature on ·OH radical scavenging activity and Fe²⁺‐chelating activity of antioxidant hydrolysates from SPP were investigated. The maximum ·OH radical scavenging activity (40.10%) and Fe²⁺‐chelating activity (74.37%) of SPP hydrolysates (SPPH) were obtained at an enzyme‐to‐substrate ratio of 4%, pH value of 7.8 and reaction temperature of 57 °C, which was in agreement with the predicted value (40.11% and 74.83%, respectively) estimated by RSM. The simulated in vitro gastrointestinal digestion (GID) dramatically modified molecular weights distribution, increased peptide (<3 kDa) concentration and highly retained antioxidant activity of SPPH, indicating potentially utilisation of SPPH as a functional supplement in food system.     

Characterisation of antioxidant peptides from enzymatic hydrolysate of golden melon seeds protein

The purpose of present research was to study novel antioxidant peptides from Golden melon seeds. Alkaline protease was used to hydrolyse the Golden melon seeds protein to obtain the hydrolysed peptides. These antioxidant peptides were purified and identified by ultrafiltration, gel filtration chromatography and RP-HPLC-ESI-MS/MS. Results showed that the peptide fraction (GMSHp3) with molecular weight (MW) <3 kDa obtained by ultrafiltration had the highest antioxidant capacity. This fraction was further purified via gel filtration chromatography into six sub-fractions, among which GMSHp3-3 exhibited the highest hydroxyl radical scavenging effect. Fraction GMSHp3-3 was further purified via RP-HPLC-ESI-MS/MS and sequenced as six potential antioxidant peptides with amino acids sequences of RMSFPVMCRN, LMRVLAQLG, ALAPLVALPAA, LVGKPAPD, LPAAHKA and AHAAGYGG, among which LMRVLAQLG, LPAAHKA and AHAAGYGG possessed effective ferric reducing power. These results indicated that novel antioxidant peptides from golden melon seeds protein hydrolysates might be potential antioxidant source of functional foods or nutraceutical supplements.     

家常烹调方法对酱油游离氨基酸的影响

以酱油为原料,采用家常烹调方法,研究蒸、煮和微波处理对酱油质量损失、游离氨基酸变化规律的影响。结果表明:经过蒸、煮和微波处理后,酱油质量均有损失。与未处理酱油相比,煮制和微波处理之后酱油中游离氨基酸总含量增多。煮制和微波处理后酱油中鲜味氨基酸浓度增加,而蒸制处理后酱油中鲜味氨基酸浓度略微减小。未处理、蒸、煮和微波处理后酱油中TAV>1的游离氨基酸分别有9,9,11,10种。经过蒸制和微波处理,酱油中必需氨基酸总量均减少,而煮制处理酱油中必需氨基酸总量增多。酱油中鲜味氨基酸、苦味氨基酸、脂肪族氨基酸、疏水性氨基酸、亲水性氨基酸、极性氨基酸、非极性氨基酸、酸性氨基酸总量在3种烹调方法处理后均减少。     

Antioxidant activity in HepG2 cells,immunomodulatory effects in RAW 264.7 cells and absorption characteristics in Caco‐2 cells of the peptide fraction isolated from Dendrobium aphyllum

DA‐P, fraction of peptides with a molecular weight <1 kDa isolated from Dendrobium aphyllum, was analysed in three types of cell lines to verify its bioactivity and absorptivity. The cellular antioxidant activity of DA‐P in HepG2 cells was used and results revealed an EC50 of 2.88 ± 0.143 mg mL^?1 and a CAA unit of 63.46 ± 2.11 μm QE/100 g peptides. DA‐P treatment enhanced the secretion of cytokines in RAW 264.7 cells. After demonstrating the presence of tight junctions in Caco‐2 monolayers, the absorption was 25.57% ± 0.016% and 19.7% ± 0.012% from different sides. The relatively high absorption indicated that the antioxidant‐relevant immune functions of DA‐P had a greater possibility to be absorbed by Caco‐2 cells. Free amino acids and LC‐MS/MS analysis indicated the degradation and expulsion of components after the absorption of DA‐P, and Ser‐Ser‐Arg was able to come across the monolayers.     

Comparative study of antioxidant and flavour characteristics of Maillard reaction products from five types of protein hydrolysates

Antioxidant, structural, and flavour characteristics of Maillard reaction products (MRPs) prepared from different hydrolysates of sweet potato protein (SPPH), potato protein (PPH), soy protein isolate (SPIH), egg white protein (EWPH), and whey protein isolate (WPIH) were compared. WPIH-MRPs exhibited the highest Maillard reaction (MR) progress followed by SPPH-MRPs as indicated by the lowest pH (4.95 and 5.10, respectively) and the highest fluorescence intensity (P < 0.05). The results of Fourier transform infrared (FTIR) explained the significant changes in functional groups of peptides after MR, especially in WPIH-MRPs and SPPH-MRPs. The highest oxygen radical absorbance capacity (ORAC) of 125.24 µg TE (Trolox equivalents)/mL was observed for WPIH-MRPs, followed by SPPH-MRPs with an ORAC value of 104.07 µg TE/mL (P < 0.05). MR conferred an increase of sweetness, sourness, and umami attributes and reduction of bitterness for all MRPs, and WPIH-MRPs presented the highest umami taste score of 7.4, followed by SPPH-MRPs with a taste score of 7.1. Stronger umami taste was correlated with MW 200–500 and <200 Da peptides. No acrylamide was detected in SPPH-MRPs, which also presented less 5-hydroxymethyl furfural (HMF) and Nε-(1-Carboxymethyl)-L-lysine (CML) compared to WPIH-MRPs. Thus, MRPs derived from SPPH could be an alternative way for natural flavours’ production with improved antioxidant activity and less harmful compounds.     

Sweet potato protein hydrolysates: antioxidant activity and protective effects on oxidative DNA damage

In this study, sweet potato protein (SPP) hydrolysates were prepared by six enzymes (alcalase, proleather FG‐F, AS1.398, neutrase, papain and pepsin). The antioxidant activities and protective effect against oxidative DNA damage of SPP hydrolysates were investigated. Alcalase hydrolysates exhibited the highest hydroxyl radical‐scavenging activity (IC₅₀ 1.74 mg mL^?1) and Fe²⁺‐chelating ability (IC₅₀ 1.54 mg mL^?1) (P < 0.05). Compared with other five hydrolysates, the hydrolysates obtained by alcalase had the most abundant <3‐kDa fractions. In addition, below 3‐kDa fractions of alcalase hydrolysates showed the highest antioxidant activities and protective effects against DNA damage through both scavenging hydroxyl radicals and chelating Fe²⁺, which was probably because of the increase in several antioxidant amino acids, such as His, Met, Cys, Tyr and Phe, as well as the hydrophobic amino acids. The results suggested that enzymatic hydrolysis could be used as an effective technique to produce high value‐added peptides products from SPP.     

Purification and identification of antioxidant peptides from corn gluten meal

Corn gluten meal was hydrolyzed by alkaline protease and Flavourzyme to obtain the antioxidant peptides. The antioxidant activities of the hydrolysates or peptides were evaluated by free radical scavenging capacity (1,1-diphenyl-2-picrylhydrazyl/2,2-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt/hydroxyl radical/superoxide radical anion), metal ion (Fe²⁺/Cu²⁺) chelating activity and lipid peroxidation inhibitory capacity. The hydrolysates were separated by ultrafiltration, and those with molecular weight <10 kDa exhibited highest antioxidant activity in all relevant assays. The hydrolysates were subsequently purified by gel filtration chromatography, and fraction F3 showed the highest antioxidant activity. Three peptides were identified from fraction F3 using LC–ESI–Q–TOF MS/MS as Leu-Pro-Phe (375.46 Da), Leu-Leu-Pro-Phe (488.64 Da) and Phe-Leu-Pro-Phe (522.64 Da). These peptides exhibited good free radical scavenging activity and lipid peroxidation inhibitory effect. Thus, corn gluten meal may be used as a potential source of antioxidant peptides for food and nutraceutical applications.     

Comparison of physicochemical properties of beef potentiators prepared by synergistic fermentation and traditional method

Beef potentiator was prepared by beef qu, which was previously prepared by a novel synergistic fermentation method (BPSF). Three kinds of other beef potentiators were prepared by commercial enzymes (protamex, flavourzyme and papain, BPCEs), which were used as controls to investigate the physicochemical properties of BPSF. Results showed that BPSF possessed a higher protein recovery (70.99%) and degree of hydrolysis (DH, 51.39%) than BPCEs. The tests of molecular weight distribution and free amino acids (FAAs) indicated that the moderate molecular weight peptides (1–5 kDa) were dominant (70.07–74.43%) in all beef potentiators. The low molecular weight peptides (<1 kDa), umami amino acids and total amino acids in BPSF, were 1.03‐ to 5.56‐, 5.25‐ to 26.50‐ and 1.57‐ to 4.79‐fold higher than those in BPCEs, respectively. Meanwhile, hierarchical cluster analysis indicated that BPSF was significantly different to BPCEs, and sensory evaluation showed that BPSF had apparently stronger umami taste than BPCEs.     

Effect of domestic cooking methods on total phenolic content,antioxidant activity and sensory characteristics of Hericium erinaceus

This study evaluated the effect of different cooking methods (microwaving, boiling, steaming and stir-frying) on the phenolic acids and antioxidant activity in Hericium erinaceus (HE). The total phenolic content (TPC) of HE decreased after cooking and was in the order of dried (control) > stir-fried > microwaved > steamed > boiled. An increase in antioxidant activity was found in all cooked HE, albeit statistically insignificant (P > 0.05). Gallic acid was reported to be the dominant phenolic acid found in HE extracts in the range of 3.03–49.41 μg g⁻¹ dry weight. Low negative correlations were observed between 2,2-diphenyl-1-picrylhydrazyl (DPPH) and TPC as well as DPPH and gallic acid profile. Sensory data revealed that stir-fried HE received the most favourable response in colour, texture, aroma and flavour attributes. Overall, this study suggested that the method of stir-frying could be used to prepare HE for better retention of gallic acid and antioxidant activity with acceptable sensory characteristics.