Transglutaminase cross-linking effect on sensory characteristics and antioxidant activities of Maillard reaction products from soybean protein hydrolysates

To improve the yield of Maillard peptides, a microbial transglutaminase (MTGase) was used to increase the content of 1000–5000 Da peptides in soybean protein hydrolysates by using a cross-linking reaction. The sensory characteristics and antioxidant activities of corresponding Maillard Reaction Products (MSPC) was then evaluated. After cross-linking treatment the content of 1000–5000 Da peptides in protein hydrolysates and the yield of Maillard peptides increased by 21.19% and 8.71%, respectively, which contributed to the improved mouthfulness of MSPC. The bitter amino acids were significantly decreased and the umami acids were markedly increased in MSPC. Volatile compounds identified by GC–MS analysis showed that the content of the important meaty flavour compounds (such as 2-methyl-3-furanthiol, bis(2-methyl-3-furyl)disulfide) of MSPC were dramatically higher than that of MRPs from uncross-linking peptides. Combined with sensory evalution, it was confirmed that MTGase cross-linking improved the flavour Characteristics and did not affect the antioxidant activity of MSPC.     

Temperature effect on the non-volatile compounds of Maillard reaction products derived from xylose–soybean peptide system: Further insights into thermal degradation and cross-linking

Solutions of soybean peptide with or without xylose were heated over a range of temperatures (80–130 °C) for 2 h to investigate the characteristics of Maillard reaction and the effect of temperature on amino acids and peptides. It was found that both peptide degradation and peptide cross-linking occurred in the Maillard reaction. The critical temperature for peptide degradation was 100 °C, and above it, peptides degraded quickly in thermal degradation system. However, in Maillard reaction system, peptides cross-linked rapidly when the temperature reached 110 °C. Bitter amino acids and peptides below 1000 Da decreased 18.44% and 28.49%, respectively, after Maillard reaction at 120 °C. On the other hand, peptides between 1000 and 5000 Da were increased significantly, nearly doubled compared to its initial hydrolysates after Maillard reaction at 120 °C. Moreover, the increase of macromolecule products was also accompanied with severe browning and pH decrement.     

Taste enhancer from the long-term ripening of miso (soybean paste)

Long-term ripened miso has a characteristic mouthfulness and continuity of flavour, which is heightened from 11 months of ripening. Focussing on its main components, changes of protein and sugar were investigated from 10 days up to 20 months of ripening. Protein and sugar changes during ripening did not correlate with sensory evaluation results. From visual observation of miso colour and colorimetric analysis of the water-soluble fraction, it was apparent that the Maillard reaction was occurring during 5–11 months of ripening. By fractionation and evaluation of umami, mouthfulness and continuity, we were able to identify a water soluble fraction of 20 month ripened miso with a molecular weight of 1000–5000 which was coloured and appeared to be a peptide that has undergone the Maillard reaction. From these results, the Maillard-reacted peptide was considered to be a key substance which gives the characteristic flavour (mouthfulness and continuity) of long-ripened miso.     

Umami taste characteristics of water extract of Doenjang, a Korean soybean paste: Low-molecular acidic peptides may be a possible clue to the taste

We investigated the taste characteristics of doenjang water extract (DWE) for component compounds that contribute to its taste. A 1% DWE solution elicited the highest umami taste ratings in a taste profile test. A 3% solution of DWE was used as substitute for 9.4% of monosodium glutamate in a taste soup base, and it masked the bitter taste of hydrolysed animal protein when mixed in solution. DWE was fractionated, based on molecular weights, and fraction IV (F-IV; 1000 > MW ? 500) had the highest peptide contents and elicited the strongest umami taste. The acidic peptide fraction of F-IV elicited the strongest umami taste. The major bound-type amino acids in DWE, F-IV and the acidic peptide fraction were Glu and Asp. These data show that the umami taste characteristics were a result of the low molecular weight acidic peptides naturally produced during the fermentation of soybeans.     

Purification and identification of kokumi-enhancing peptides from chicken protein hydrolysate

The Maillard reaction products (MRPs) from chicken protein hydrolysate were demonstrated to have intense umami and kokumi-enhancing effects. To find the main flavour-enhancing compounds in the chicken protein hydrolysate, the fractions with different molecular weights were obtained by ultrafitration. The evaluation of taste characteristics revealed that the fractions with molecular weights ranging from 1000 to 5000 Da predominantly contributed to the umami and kokumi-enhancing effects. After further purification by using ultrafiltration, gel filtration chromatography, and ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in combination with sensory evaluation, three peptides were identified, an octapeptide (WVNEEDHL), a nonapeptide (NSLEGEFKG) and a decapeptide (KDLFDPVIQD). Sensory evaluation results showed that all three peptides could significantly enhance the meat flavour, umami taste and thickness of the chicken powder solution. The results indicate that the peptides have potential application as effective chicken flavour-enhancing ingredients in the food industry.     

Electroseparation of an antibacterial peptide fraction from snow crab by-products hydrolysate by electrodialysis with ultrafiltration membranes

Recently, a snow crab by-products hydrolysate has demonstrated antibacterial properties due to a peptide with a molecular weight of about 800 Da, but only at high concentration. Consequently, peptide hydrolysate has been fractionated to obtain peptides in a more purified form. The aim of this work was to separate a snow crab by-products hydrolysate by electrodialysis with ultrafiltration membranes (EDUF). EDUF, which allows separation of molecules according to their charges and molecular weights, was used to recover and concentrate the active antibacterial fraction. Two different ultrafiltration membranes (20 and 50 kDa) and two electrical field strengths (2 and 14 V/cm) were used as separation parameters. After EDUF separation, the 300-600 Da peptide molecular weight range was the most recovered with an abundance of 94%. Moreover, fractionation at 14 V/cm with ultrafiltration membranes of 50 kDa allowed the recovery of an anionic fraction which showed antibacterial properties on Escherichia coli ATCC 25922 and Listeria innocua HPB 13.     

不同分子质量大豆蛋白和鸡肉酶解物的美拉德反应产物风味特征分析

为了研究不同分子质量的肽在美拉德反应后的风味特征,以大豆蛋白和鸡肉为原料酶解得到蛋白酶解物。对酶解物超滤分离得到小于1000Da、1000~5000Da和大于5000Da的不同分子质量肽组分,并对大豆蛋白和鸡肉酶解物完全酸水解得到复合氨基酸。在得到的肽段和氨基酸中添加一定量的木糖,构建美拉德反应模型。对美拉德反应产物感官特性进行评价,再采用气相色谱-质谱联用、高效液相色谱对挥发性和不挥发性化合物进行分析。结果表明:在2种不同蛋白来源的酶解物的美拉德反应产物中,共鉴定出挥发性化合物69种,其中吡嗪和呋喃硫醇等肉香味化合物的含量最高。统计分析表明:不同分子质量的肽和游离氨基酸的挥发性化合物存在明显差异。小于1000Da的肽在美拉德反应过程促进了吡嗪类化合物的生成,其中包括了吡嗪、5-甲基-2-乙基吡嗪、2,5-二甲基-3-乙基吡嗪、三甲基吡嗪、2-乙酰基吡咯等挥发性化合物。与肽相比,游离氨基酸有利于含硫化合物如呋喃硫醇类和噻吩类物质的生成。有29种挥发性化合物的相对气味活性值大于1。偏最小二乘回归研究了气味化合物与感官评价之间的相关性,发现小于1000Da的肽与基本的肉味和浓厚味密切相关,而大于5000Da的肽与苦味和焦煳味密切相关。在美拉德反应后,分子质量大于5000Da的肽数量显著减少；分子质量1000~5000Da的肽降解可以补充消耗的游离氨基酸；分子质量小于1000Da的肽容易发生交联和聚合现象而含量增加,其产物对风味的影响明显增强,能更好地体现基本的肉味、鲜味和浓厚味。希望研究可以为利用蛋白质酶解物生产美拉德反应产物的应用提供理论支撑和指导。     

Sensory Characteristics and Antioxidant Activities of Maillard Reaction Products from Soy Protein Hydrolysates with Different Molecular Weight Distribution

Soy protein was hydrolyzed using two enzymes to obtain soy protein hydrolysate (SPH), the SPH was fractionated with ultrafiltration membranes to obtain peptide fractions below 1,000 Da (SP1) and 1,000–5,000 Da (SP2), and for the meantime, SPH was further completely hydrolyzed to get compound amino acids (CAA). Maillard reaction products (MRPs) were prepared from aqueous xylose–SPH/SP1/SP2/CAA model systems by heating at 120°C for 2.0 h. Compared with the original hydrolysates and other MRPs, the MRPs from SP2 exhibited a distinctly enhanced effect on flavor, including the caramel-like, soy sauce-like odors, umami and mouthful tastes and a greatly reduced bitterness in consomme′ soup. Antioxidant activities of SPH, SP1, SP2, CAA, and their MRPs were investigated through reducing power, DPPH radical-scavenging activity, and Fe²⁺ chelating activity. Before Maillard reaction, the antioxidant activities of peptide fractions with different molecular weights were quite different, and SP2 showed the highest activity; however, CAA exhibited very poor antioxidant activity. The antioxidant activities of SPH, SP1, SP2, and CAA were greatly enhanced by Maillard reaction, and the MRPs prepared from xylose–CAA model system exhibited a higher antioxidant activity than those from other model systems. Pyrazines, pyrroles, furans, and thiazoles were significantly correlated with reducing power and Fe²⁺ chelating activity by principal component analysis.     

Effects of ultrasound-assisted enzymatic hydrolysis and monosaccharides on structural,antioxidant and flavour characteristics of Maillard reaction products from sweet potato protein hydrolysates

Effects of ultrasound (US)-assisted enzymatic hydrolysis and different monosaccharides (arabinose; xylose, XY; galactose and glucose) on peptide structure, antioxidant activities and flavour characteristics of Maillard reaction products (MRP) from sweet potato protein hydrolysates were investigated. US markedly enhanced the MR progress, and USXY showed the lowest pH value of 5.04, the highest browning intensity and fluorescence intensity (P < 0.05). FTIR results revealed significant peptide structure changes in USXY, USAR and USGA compared to other samples. USXY exhibited the highest Oxygen radical absorbance capacity (ORAC) value of 109.15 µg TE/mL, followed by USGA and USAR (94.07 and 93.41 µg TE/mL), respectively (P < 0.05). USXY and USAR showed different aroma features as compared to other MRP (P < 0.05). In addition, US enhanced umami, sweetness and sourness attributes and reduced bitterness of all MRP. USXY exhibited the highest umami intensity score (7.4), followed by USGA (7.3) and USAR (7.2), respectively. Partial least square regression analysis showed that the stronger umami taste was strongly correlated to aldehydes, thiophenes, MW 1000–3000 and 500–1000 Da peptides. Thus, US-assisted enzymatic hydrolysis and MR with xylose (XY) could be a promising way to produce natural flavouring with improved antioxidant activity.     

A novel angiotensin I converting enzyme inhibitory peptide from tuna frame protein hydrolysate and its antihypertensive effect in spontaneously hypertensive rats

Tuna frame protein was hydrolysed using Alcalase, Neutrase, pepsin, papain, α-chymotrypsin and trypsin. Peptic hydrolysate exhibited the highest ACE I inhibitory activity among them and was fractionated into three ranges of molecular weight (below 1, 1–5 and 5–10 kDa) using an ultrafiltration membrane bioreactor system. The 1–5 kDa fraction showed the highest ACE inhibitory activity and was used for subsequent purification steps. During consecutive purification, a potent ACE inhibitory peptide from tuna frame protein (PTFP), which was composed of 21 amino acids, Gly-Asp-Leu-Gly-Lys-Thr-Thr-Thr-Val-Ser-Asn-Trp-Ser-Pro-Pro-Lys-Try-Lys-Asp-Thr-Pro (MW: 2,482 Da, IC₅₀: 11.28 μm), was isolated. Lineweaver–Burk plots suggest that PTFP plays as a non-competitive inhibitor against ACE. Furthermore, antihypertensive effect in spontaneously hypertensive rats (SHR) also revealed that oral administration of PTFP can decrease systolic blood pressure significantly (P < 0.01). These results suggest that the PTFP would be a beneficial ingredient for nutraceuticals and pharmaceuticals against hypertension and its related diseases.     

Enhancing the anti-adipogenic activity of soy protein by limited hydrolysis with Flavourzyme and ultrafiltration

Limited hydrolysis of soy protein isolate (SPI) with Flavourzyme for 2 h to obtain the hydrolysate (FH2h) revealed much higher suppression of glycerol-3-phosphate dehydrogenase (GPDH) activity and relative lipid accumulation (RLA) than intact SPI in 3T3-L1 preadipocytes during differentiation. Lower GPDH activity or RLA indicates higher anti-adipogenic activity. The GPDH significantly decreased from 673 to 477 U/mg protein (p < 0.05). Sequentially fractionating FH2h with 30–1 kDa (kilo-daltons) molecular weight cut-off (MWCO) membranes to obtain the 1 kDa permeate resulted in further reduction of 59% GPDH activity. When comparing the high-performance size-exclusion chromatography (HPSEC) profiles, the most active peptide fraction for the anti-adipogenic activity was primarily composed of small peptides with molecular weight less than 1300 Da. According to the Western immunoblot analysis, 1 kDa permeate inhibits adipogenesis by affecting the expression of peroxisome proliferators-activated receptor γ (PPARγ) and the CCAAT/enhancer binding protein α (C/EBPα) during 3T3-L1 cells differentiation.     

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.     

Antioxidant activity of vinegar melanoidins

Melanoidins, the brown polymers formed through Maillard reaction during vinegar process, are one of major high-molecular-weight fractions of vinegar. In this study the antioxidant activity of high-molecular-weight fractions (MW > 3500 Da) separated from ethanol-supernatant extraction of concentrated Zhenjiang aromatic vinegar was evaluated by different in vitro tests: the DPPH radical scavenging activity, the reducing power, total phenolic content, and the inhibitory effect on hydroxyl radical. Each individual fraction was found to have antioxidant activity in all the model systems tested. The high-molecular-weight fractions of vinegar (MW > 3500 Da) were separated into different fractions by DEAE-Sepharose fast flow. The fractions eluted by 0.2 mol/L NaCl and 0.3 mol/L NaCl with higher phenolic content have stronger DPPH radical scavenging activity and reducing power. Antioxidant activity in hydroxyl radical system was not correlated with phenolic content. Two phases which have stronger effects on Maillard reaction products (MRPs) in production process were examined. Decoction, storing and aging may affect vinegar’s antioxidant activity. The present results support the concept that melanoidins formed during vinegar production process may have health promotion activity.     

Value-added utilization of yak milk casein for the production of angiotensin-I-converting enzyme inhibitory peptides

Yak (Bos grunniens) milk casein derived from Qula, a kind of acid curd cheese from northwestern China, was hydrolysed with alcalase. The hydrolysates collected at different hydrolysis times (0 min, 60 min, 120 min, 180 min, 240 min, 300 min, 360 min) were assayed for the inhibitory activity of angiotensin-I-converting enzyme (ACE), and the one obtained at 240 min hydrolysis showed the highest ACE inhibitory activity. The active hydrolysate was further consecutively separated by ultrafiltration with 10 kDa and then with 6 kDa molecular weight cut-off membranes into different parts, and the 6 kDa permeate showed the highest ACE-inhibiting activity. This active fraction was further purified to yield two novel ACE-inhibiting peptides, whose amino acid sequences were Pro–Pro–Glu–Ile–Asn (PPEIN)(κ-CN; f156–160) and Pro–Leu–Pro–Leu–Leu (PLPLL) (β-CN; f136–140), respectively. The molecular weight and IC₅₀ value of the peptides were 550 Da and 566.4 Da, and 0.29 ± 0.01 mg/ml and 0.25 ± 0.01 mg/ml, respectively.     

Detection of early bruises in apples using hyperspectral data and thermal imaging

The early detection of bruises in apples was studied using a system that included hyperspectral cameras equipped with sensors working in the visible and near-infrared (400–1000 nm), short wavelength infrared (1000–2500 nm) and thermal imaging camera in mid-wavelength infrared (3500–5000 nm) ranges. The principal components analysis (PCA) and minimum noise fraction (MNF) analyses of the images that were captured in particular ranges made it possible to distinguish between areas with defects in the tissue and the sound ones. The fast Fourier analysis of the image sequences after pulse heating of the fruit surface provided additional information not only about the position of the area of damaged tissue but also about its depth. The comparison of the results obtained with supervised classification methods, including soft independent modelling of class analogy (SIMCA), linear discriminant analysis (LDA) and support vector machines (SVM) confirmed that broad spectrum range (400–5000 nm) of fruit surface imaging can improve the detection of early bruises with varying depths.     

Flavour components and antioxidant properties of several cultivated mushrooms

Three mushrooms, Clitocybe maxima, Pleurotus ferulae and Pleurotus ostreatus grey strain were used to study their flavour components and antioxidant properties. The volatile flavour components found comprised of six eight-membered carbon compounds and two aromatic compounds. The content total of soluble sugars and polyols was 125–270 mg/g. The content of monosodium glutamate-like components was 1.76–8.89 mg/g. The contents of flavour 5′-nucleotides ranged from 1.89 to 7.59 mg/g. Based on the results obtained, three mushrooms possessed highly intense umami taste. Ethanolic extracts were more effective in the inhibition of conjugated diene and scavenging ability on 1,1-diphenyl-2-picrylhydrazyl radicals, whereas hot water extracts were more effective in the scavenging ability of hydroxyl radicals. EC₅₀ values were less than 14 and 30 mg/ml for ethanolic and hot water extracts, respectively, indicating that the three mushrooms were relatively effective as they exhibited antioxidant properties, despite having scavenging abilities for hydroxyl radicals. Phenols were the major antioxidant components and the total contents were 5.10–11.1 mg gallic acid equivalents/g.     

Characteristics and antioxidant activity of ultrafiltrated Maillard reaction products from a casein–glucose model system

Maillard reaction products (MRPs) were prepared from casein–glucose by refluxing for 130 min at 102 °C and initial pH 12.0 without pH control to investigate the characteristics of casein–glucose Maillard reaction and the antioxidant activity difference among different fractions of MRPs. Browning and intermediate products increased, however, the pH of the system decreased with increase in the heating time. Free amino group content decreased 78% during first 10 min and did not change nearly thereafter. Amino acid analysis indicated that lysine and arginine decreased significantly, and casein was partially hydrolysed to peptides or free amino acid. High molecular weight compounds were dominant in the MRPs, determined by high performance gel-filtration chromatography. After ultrafiltration, antioxidant activity of each MRPs fraction was investigated by DPPH radical-scavenging activity, reducing power, Fe²⁺ chelating activity and lecithin oxidation assay. MRPs of different molecular weight exhibited distinctly different antioxidant activities.     

Contribution of sulfur-containing compounds to the colour-inhibiting effect and improved antioxidant activity of Maillard reaction products of soybean protein hydrolysates

BACKGROUND: Light‐coloured and savoury‐tasting flavour enhancers are attractive to both consumers and food producers. The aim of this study was to investigate the colour‐inhibiting effect of L ‐cysteine and thiamine during the Maillard reaction of soybean peptide and D ‐xylose. The correlation between volatile compounds and antioxidant activity of the corresponding products was also studied. RESULTS: Colour formation was markedly suppressed by cysteine. Compared with peptide/xylose (PX), the taste profile of Maillard reaction products (MRPs) derived from peptide/xylose/cysteine (PXC) and peptide/xylose/cysteine/thiamine (PXCT) was stronger, including umami, mouthfulness, continuity, meaty and overall acceptance. PXC and PXCT also exihibited distinctly higher antioxidant activity. Principal component analysis was applied to investigate the correlation between antioxidant activity and volatile compounds. Of 88 volatile compounds identified, 55 were significantly correlated with antioxidant activity by two principal components (accounting for 85.05% of the total variance). CONCLUSION: Effective colour control of the Maillard reaction by L ‐cysteine may allow the production of healthier (higher antioxidant activity) and tastier foods to satisfy consumers' and food producers' demands. Light‐coloured products might be used as functional flavour enhancers in various food systems. Copyright © 2010 Society of Chemical Industry     

An analysis of Maillard reaction products in ethanolic glucose–glycine solution

The present study compared the Maillard reaction products in ethanolic and aqueous glucose–glycine solutions. The pH 4.3, 0.2 M glucose–0.2 M glycine solutions were prepared and heated. HPLC-DAD (diode array detection) was then used to analyse the browned solutions, the ethyl acetate extracts of the solutions, and the coloured bands in TLC of the extracts. HMF (5-hydroxymethyl-2-furaldehyde) was found in both of the browned aqueous and ethanolic solutions, while 2-hydroxymethylfuran was found only in the browned ethanolic solution. HMF and 2-acetylpyrrole appear in the ethyl acetate extract of both systems, whereas 2-acetyl-1-methylpyrrole is present only in the extract of the ethanolic solution. The difference in profile of products in the aqueous and the ethanolic solutions indicates that the mechanisms of Maillard reaction in these two systems are not exactly the same.     

Angiotensin I-converting enzyme inhibitor derived from soy protein hydrolysate and produced by using membrane reactor

Five different proteolytic enzymes, including Alcalase, Flavourzyme, trypsin, chymotrypsin and pepsin were employed to hydrolyze isolated soy protein (ISP) to produce the hydrolysates, respectively. The result indicated that hydrolysis of ISP for 0.5–6 h with Alcalase produced the highest ACE inhibitory activity. Therefore, Alcalase was selected for further study on optimization of hydrolysis conditions. The optimum conditions for Alcalase to hydrolyze ISP to produce the lowest IC₅₀ value were: E/S = 0.01, hydrolysis temperature = 50 °C, pH 9.0 and hydrolysis time = 6 h. Under these conditions, the IC₅₀ value of ISP was significantly reduced from 66.4 to 0.67 mg protein/ml. The lower IC₅₀ value represented the higher the ACE inhibitory activity. Moreover, several membranes with molecular weight cut-offs (MWCFs) of 1000–30,000Da were used to filter the hydrolysate. The 10 kDa permeate obtained from the treatment of the hydrolysate by 10,000 Da MWCF membrane could further reduce its IC₅₀ value from 0.668 to 0.078 mg protein/ml with a peptide recovery of 67.5%. An operation stability study showed that the membrane reactor system could maintain a steady production of ISP hydrolysate for over 8 h. The in vitro effect of gastrointestinal protease on ACE inhibitory activity of 10 kDa permeate was also investigated. The results suggested that gastrointestinal proteases have very little effect on the ACE inhibitory activity of 10 kDa permeate.