Bioactive peptides from brown rice protein hydrolyzed by bromelain: Relationship between biofunctional activities and flavor characteristics

This study evaluated the biological properties of peptides from brown rice protein hydrolyzed by bromelain (eb-RPH) in relation to flavor characteristic. The fractionation into peptides < 1 kDa was observed to improve the DPPH, ABTS, and hydroxyl radical-scavenging activities (0.19, 2.28, and 24.64 mM Trolox, respectively), angiotensin-converting enzyme (ACE)-inhibitory activity (IC₅₀ value of 0.20 ± 0.011 mg protein/mL), as well as bitter and umami tastes. The < 1 kDa fraction was further analyzed by liquid chromatography-electrospray ionization/mass spectrometry to identify amino acid sequence associated with biological activities and flavor characteristics. Eight peptides were identified. Most of the identified peptides contained features of previously reported ACE inhibitory and antioxidant peptides, especially peptide FGGSGGPGG and FGGGGAGAGG. Evaluation of flavor characteristics using BIOPEP database demonstrated that they had high occurrence frequencies of umami peptides (ESDVVSDL, GSGVGGAK, and SSVGGGSAG) and low Q-value (938.75 to 282.22), suggesting that these peptides may be used as a fortifying health ingredient with good taste. PRACTICAL APPLICATION: The fractionated brown rice protein hydrolysate (< 1 kDa) has the potential to serve as a functional food ingredient in nutraceutical food and beverage products that can provide health benefits with good taste. Information on amino acid composition and spatial conformation of peptide may aid us to better understand the molecular mechanisms involved in bioactivities and flavor of brown rice peptide for industrial applications.

Changes in physico-chemical, astringency, volatile compounds and antioxidant activity of fresh and concentrated cashew apple juice fermented with Lactobacillus plantarum

Changes in physico-chemical qualities (pH, total acidity, total and reducing sugar, total phenolic and vitamin C), astringency compounds (condensed and hydrolysable tannin), antioxidant activities [2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical] and flavor volatile compounds in Lactobacillus plantarum-fermented cashew-apple-juice (CAJ) and 11.4 °Bx concentrated-cashew-apple-juice (CCAJ) was investigated. Total phenolics remained unchanged throughout fermentation period, whereas condensed tannins increased and hydrolysable tannins decreased indicating reduced astringency compounds. Antioxidant activity based on both DPPH and ABTS radical scavenging activities marginally declined in some stages but overall were sustained during fermentation. Although the DPPH· radical based antioxidant activity of fermented CAJ was greater than that of fermented 11.4 °Bx CCAJ, a higher ABTS·+ radical scavenging activity was found in fermented 11.4 °Bx CCAJ, reflecting higher water soluble antioxidants. Results also indicated that DPPH· radical scavenging activity was positively correlated to vitamin-C and condensed tannins but not hydrolysable tannins. ABTS·+ radical scavenging activity was also positively correlated to condensed tannins and not hydrolysable tannins. The vitamin-C that increased during initial 12 h fermentation, decreased from 2516 to 2150 mg AAE/L at the end of 72 h fermentation. Fermented CAJ had a remarkable sweet aroma with a fruity note of two major compounds; 3-methyl-1-butanol (14.20 × 107) and 2,6-dimethyl-4-heptanol (14.76 × 107). The high phytochemicals and volatile compounds in fermented CAJ indicated that it could serve as a functional beverage with potential health benefits with reduced astringency due to lower hydrolysable tannins.

Assessment of antioxidant properties of membrane ultrafiltration peptides from mungbean meal protein hydrolysates

BACKGROUND

Bioactive peptides can prevent damage associated with oxidative stress in humans when consumed regularly. Recently, peptides have attracted immense interest because of their beneficial functional properties, safety and little or no side effects when used at high concentration. Most antioxidant peptides are small in size, less than 1 kDa, and contains a high proportion of hydrophobic amino acid. Particularly, tyrosine, leucine, alanine, isoleucine, valine, lysine, phenyalanine, cysteine, methionine and histidine in peptide chain exhibited high antioxidant activity. Mungbean meal protein (MMP) is highly abundant in hydrophobic amino acids. It indicated that MMP might be a good source of antioxidants. Therefore, the objectives were to optimize the conditions used to generate mungbean meal protein hydrolysate (MMPH) with antioxidant activity from bromelain and to investigate the antioxidant activities of different molecular weight (MW) peptide fraction.

METHODS

Response Surface Methodology (RSM) was used for screening of the optimal conditions to produce MMPH. After that MMPH was fractionated using ultrafiltration membranes with different MW distributions. Crude-MMPH and four fractions were investigated for five antioxidant activities: 2,2,1-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, superoxide, ferric reducing antioxidant power (FRAP) and metal ion chelation activity.

RESULTS

The optimal condition to produce the MMPH was 15% (w/w) of bromelain and hydrolysis time for 12 h which showed the greatest DPPH and ABTS radical scavenging activity. After mungbean protein from optimal condition was separated based on different molecular weight, the DPPH radical scavenging activity was the highest for the F4 (less than 1 kDa) peptide fraction. Metal ion chelating activity was generally weak, except for the F4 that had a value of 43.94% at a protein concentration of 5 mg/mL. The F4 also exhibited high hydroxyl and superoxide activities (54 and 65.1%), but moderate activity for ferric reducing antioxidant power (0.102 mmole Fe2+/g protein) compared to other peptide fractions and crude-MMPH. Molecular weight and amino acid were the main factors that determined the antioxidant activities of these peptide fractions. Results indicated that F4 had strong antioxidant potentials.

DISCUSSION

The lowest MW fraction (less than 1 kDa) contributed to the highest DPPH, superoxide, hydroxyl and metal chelation activity because influence of low MW and high content of hydrophobic amino acid in peptide chain. Results from this study indicated that MMPH peptides donate protons to free radicals because they had significantly high DPPH value compared to superoxide, hydroxyl and FRAP, which reactions were electron donation. Moreover, MMPH peptides had the ability to inhibit transition metal ions because of highly abundant glutamic acid and aspartic acid in peptide chain.

Isolation and characterisation of antioxidative peptides from bromelain-hydrolysed brown rice protein by proteomic technique

In this study, proteins from Thai brown rice (Khao Dawk Mali 105) were separated into albumin (2.18 %), globulin (3.98 %), glutelin (84.23 %), and prolamin (9.61 %) fractions, and were hydrolysed with various bromelain concentrations and hydrolysis times. Liquid chromatography-electrospray ionization/mass spectrometry (LC-ESI-MS/MS) was conducted to assess the composition, molecular weight (MW) distribution, and sequence of the resulting peptides, and showed that most peptides have a MW below 2000 Da (60-70 %). Glutelin fraction hydrolysates exhibited the highest 2,2'-azino-bis 3-ethylbenzthiazoline-6-sulfonic (ABTS•+) radical-scavenging (0.69 ± 0.04 µM trolox) and copper chelating (4.12 ± 0.01 mg ethylenediaminetetraacetic acid; EDTA) activities, which was further fractionated into six fractions using reversed-phase high-performance liquid chromatography. The fourth fraction showed the highest ABTS•+ scavenging (1.08 ± 0.03 mM trolox) and copper chelating (5.00 ± 0.02 mg EDTA) activity. LC-MS/MS analysis revealed that the peptides with MW less than 1500 Da and hydrophobic or aromatic N-terminal residues, such as SPFWNINAHS, MPVDVIANAYR, VVYFDQTQAQA, and VEVGGGARAP, possibly contributed to the highest antioxidant activity in fourth fraction.

Development of smart colourimetric starch-based indicator for liberated volatiles during durian ripeness

The mechanical, physical and barrier properties of colourimetric starch-based films (CSBFs) were developed by adding natural polymers (chitosan, citric acid, carboxymethylcellulose, and kraft fibre). Novel volatile compound indicator films were prepared from starch (as a film matrix with 30% w/w sorbitol) using the casting method and adding natural polymers, and pH-dye (methyl red and bromothymol blue as indicators). CSBFs mixed with 0.1% chitosan improved the mechanical and barrier properties with a significant decrease in water vapour transmission rate, water solubility, and oxygen transmission rate, as well as improved tensile strength. Trials using liberated fruit aromas verified that CSBFs resulted in visible colour changes in the presence of mixed sulphur and ethyl alcohol aromas. Colour change in terms of the total colour difference of CSBFs was related to mixed sulphur and ethyl alcohol levels, thereby enabling CSBFs could be used to monitor real-time ripeness of durian volatiles.

A novel multi-biofunctional protein from brown rice hydrolysed by endo/endo-exoproteases

Brown rice, which is a less allergenic food grain and contains essential amino acids, was hydrolysed by bromelain and PROTEASE FP51® to improve its functionalities and taste for food applications. The hydrolysate prepared by bromelain (eb-RPH) had high protein solubility, surface hydrophobicity, low molecular weight peptides, hydrophobic amino acids (leucine, valine and glycine) and flavor amino acids (glutamic acid and aspartic acid). The eb-RPH exhibited higher 1,1-diphenyl-2-picrylhydrazyl (DPPH˙) and 2,2'-azino-bis 3-ethylbenzthiazoline-6-sulfonic (ABTS˙(+)) radical-scavenging activities of 76.62% and 52.96%, respectively, and possessed a better foaming capacity (221.76%) and emulsifying capacity (32.34%) than the hydrolysate prepared by PROTEASE FP51® (ep-RPH) did. The eb-RPH gave the desired taste, which is attributed to volatile flavor compounds (benzaldehyde, benzeneacetaldehyde and 2-acetyl-1-pyrroline) and non-volatile flavor compounds, such as monosodium glutamate, 5'-guanosine monophosphate and 5'-inosine monophosphate (0.07, 0.03 and 0.05 mg mL(-1), respectively). Brown rice peptides generated by bromelain were novel bioactive peptides with multifunctional properties.

Physicochemical and flavor characteristics of flavoring agent from mungbean protein hydrolyzed by bromelain

Enzymatic bromelain mungbean meal protein hydrolysate (eb-MPH) was produced from mungbean meal protein isolate (MPI). Enzymatic bromelain, with a known protease activity of 98,652 (unit/g), was used at concentrations of 0, 2, 6, 10, 14 and 18% (w/w) and with hydrolysis times of 0.5, 3, 6, 12, and 24 h. The pH and temperature were controlled at 6.0 and 50 °C, respectively. It was found that the best treatment combination for eb-MPH production by response surface methodology (RSM) was 18% bromelain and a hydrolysis time of 3 h, resulting in the greatest degree of hydrolysis (% DH) and percent yield, with values of 61.04 and 45.63%, respectively. Results also showed that the phenylalanine, tyrosine and leucine contents of the optimally produced eb-MPH were 20.88, 14.50 and 10.93%, respectively. Twelve volatile compounds were identified using gas chromatography mass spectrometry in eb-MPH; benzaldehyde, 2-pentylfuran and furfural were the predominant odorants.

Postharvest characteristics and handling of litchi fruit — an overview

Litchi (Litchi chinensis Sonn.) is a tropical to subtropical crop that originated in South-East Asia. Litchi fruit are prized on the world market for their flavour, semi-translucent white aril and attractive red skin. Litchi is now grown commercially in many countries and production in Australia, China, Israel, South Africa and Thailand has expanded markedly in recent years. Increased production has made significant contributions to economic development in these countries, especially those in South-East Asia. Non-climacteric litchi fruit are harvested at their visual and organoleptic optimum. They are highly perishable and, consequently, have a short life that limits marketability and potential expansion of demand. Pericarp browning and pathological decay are common and important defects of harvested litchi fruit. Postharvest technologies have been developed to reduce these defects. These technologies involve cooling and heating the fruit, use of various packages and packaging materials and the application of fungicides and other chemicals. Through the use of fungicides and refrigeration, litchi fruit have a storage life of about 30 days. However, when they are removed from storage, their shelf life at ambient temperature is very short due to pericarp browning and fruit rotting. Low temperature acclimation or use of chitsoan as a coating can extend the shelf life. Sulfur dioxide fumigation effectively reduces pericarp browning, but approval from Europe, Australia and Japan for this chemical is likely to be withdrawn due to concerns over sulfur residues in fumigated fruit. Thus, sulfur-free postharvest treatments that maintain fruit skin colour are increasingly important. Alternatives to SO2 fumigation for control of pericarp browning and fruit rotting are pre-storage pathogen management, anoxia treatment, and dipping in 2% hydrogen chloride solution for 6−8 min following storage at 0°C. Insect disinfestation has become increasingly important for the expansion of export markets because of quarantine issues associated with some fruit fly species. Thus, effective disinfestation protocols need to be developed. Heat treatment has shown promise as a quarantine technology, but it injures pericarp tissue and results in skin browning. However, heat treatment can be combined with an acid dip treatment that inhibits browning. Therefore, the primary aim of postharvest litchi research remains the achievement of highly coloured fruit which is free of pests and disease. Future research should focus on disease control before harvest, combined acid and heat treatments after harvest and careful temperature management during storage and transport.