Yongkang Luo

Milk processing as a tool to reduce cow’s milk allergenicity: a mini-review

Milk processing technologies for the control of cow’s milk protein allergens are reviewed in this paper. Cow’s milk is a high nutritious food; however, it is also one of the most common food allergens. The major allergens from cow’s milk have been found to be β-lactoglobulin, α-lactalbumin and caseins. Strategies for destroying or modifying these allergens to eliminate milk allergy are being sought by scientists all over the world. In this paper, the main processing technologies used to prevent and eliminate cow’s milk allergy are presented and discussed, including heat treatment, glycation reaction, high pressure, enzymatic hydrolysis and lactic acid fermentation. Additionally, how regulating and optimizing the processing conditions can help reduce cow’s milk protein allergenicity is being investigated. These strategies should provide valuable support for the development of hypoallergenic milk products in the future.

Effects of fermentation by lactic acid bacteria on the antigenicity of bovine whey proteins.

BACKGROUNDnThe main whey proteins alpha-lactalbumin (alpha-LA) and beta-lactoglobulin (beta-LG) are considered as the major allergens in cows milk. Microbial fermentation can produce some proteolytic enzymes, which can induce the degradation of milk protein allergens. In this study, the effects of fermentation by lactic acid bacteria on the antigenicity of alpha-LA and beta-LG were investigated using indirect competitive ELISA. Meanwhile, the proteolysis of milk proteins was detected by TNBS assay and SDS-PAGE electrophoresis.nnnRESULTSnFermentation by lactic acid bacteria could significantly reduce the antigenicity of alpha-LA and beta-LG in skim milk. Combined strains of Lactobacillus helveticus and Streptococcus thermophilus were the most effective in reducing the antigenicity of both whey proteins. In addition, alpha-LA and beta-LG antigenicity decreased to a lower value at 6 h of fermentation and at 0.5 d of cold storage by fermentation with the combined strains. The results of TNBS assay and SDS-PAGE electrophoresis showed that lactic acid bacteria strains used in this study hydrolysed whey proteins only to a limited extent.nnnCONCLUSIONnThe fermentation with lactic acid bacteria is an effective way to reduce whey proteins antigenicity.

Biochemical, sensory and microbiological attributes of bream (Megalobrama amblycephala) during partial freezing and chilled storage

BACKGROUNDnBream is one of the main farmed freshwater fish species in China. This study aimed to examine the nucleotide degradation of bream during partial freezing and chilled storage and to assess the possible usefulness of nucleotide ratios (K, Ki, H, P, Fr and G values) as freshness indices in comparison with sensory assessment and total viable counts.nnnRESULTSnTotal viable counts were 5.74 and 4.66 log(colony-forming units g(-1)) on the day of sensory rejection under chilled storage and partial freezing storage respectively. The inosine 5-monophosphate decrease and inosine increase were faster in chilled storage than in partial freezing storage. Hypoxanthine levels increased continuously with time under both storage regimes. Among the nucleotide ratios, the K, Ki, P, G and Fr values were superior to the H value and provided useful freshness indicators for both storage conditions.nnnCONCLUSIONnBream in chilled storage were sensorially acceptable only up to 10 days, compared with 33 days for bream in partial freezing storage. Partial freezing delayed the nucleotide degradation of bream.

Changes in biogenic amines of silver carp (Hypophthalmichthys molitrix) fillets stored at different temperatures and their relation to total volatile base nitrogen, microbiological and sensory score.

BACKGROUNDnBiogenic amines have received considerable attention owing to their undesirable effects in humans. There are few studies of changes in biogenic amine contents related to freshwater fish. Silver carp is an important freshwater fish species in China. This study aimed to investigate the changes in biogenic amines and their relation to total volatile base nitrogen (TVB-N), microbiological and sensory score of silver carp fillets stored at 0, 3 and 15 °C.nnnRESULTSnThe total biogenic amine contents of all silver carp fillets (regardless of storage time and temperature) ranged from 13.05 to 318.10 mg kg(-1). Putrescine and histamine were the main biogenic amines in silver carp fillets during storage. Cadaverine was only detected after 12 days at 3 °C and after 2 days at 15 °C. Spermidine and spermine contents increased during the early storage period and then slightly decreased.nnnCONCLUSIONnLow temperature could control the quality of silver carp fillets by inhibiting the contents of biogenic amines. Putrescine showed significant correlation with TVB-N, total aerobic content, sensory score, tryptamine and phenylethylamine. Putrescine was a good quality marker of silver carp fillets in the cold chain.

Antioxidant activities and functional properties of grass carp (Ctenopharyngodon idellus) protein hydrolysates

BACKGROUNDnGrass carp, with an annual production exceeding 4 × 10(6) t in China in 2009, has not been developed into a high-value product. In this study the antioxidant activities and functional properties of grass carp protein hydrolysates prepared with Alcalase 2.4L (HA) and papain (HP) were investigated. The hydrolysate with strongest radical-scavenging activity and reducing power was assessed further for changes in its antioxidant activity during simulated gastrointestinal digestion.nnnRESULTSnAs the degree of hydrolysis (DH) increased, the metal-chelating activity of both HA and HP increased while their reducing power and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH(•) )-scavenging activity decreased (P < 0.05). At the same DH, HP possessed higher DPPH(•) -scavenging activity and reducing power than HA (P < 0.05). The metal-chelating activity of HP with 10% DH was significantly increased after in vitro gastrointestinal metabolism (P < 0.05). Regarding their functional properties, all hydrolysates were more than 81% soluble over a wide range of pH (3-8). At the same DH, HP showed higher emulsion activity index but lower solubility and foaming capacity than HA.nnnCONCLUSIONnGrass carp protein hydrolysates showed high solubility over a wide pH range and could be used as natural antioxidants in food systems.

Reduced antigenicity of β-lactoglobulin by conjugation with glucose through controlled Maillard reaction conditions

Abstract The effect of weight ratio of protein to sugar (0.17–7.83), temperature (40–60°C) and time (24–120 h) on the antigenicity of β-lactoglobulin (β-LG) in conjugates of whey protein isolate (WPI) with glucose was investigated. Response surface methodology was used to carry out an optimisation of the reaction conditions leading to the minimum antigenicity of β-LG. Conjugation of WPI with glucose could reduce effectively the antigenicity of β-LG. This reduction of antigenicity could be controlled by regulating three independent variables (weight ratio of WPI to glucose, temperature and time). The model for optimal reaction conditions of a lower antigenicity of β-LG was established. Weight ratio of WPI to glucose had the greatest effect on the antigenicity of β-LG. Reaction time influenced the antigenicity of β-LG to a lesser extent.

Effects of pH, temperature, enzyme-to-substrate ratio and reaction time on the antigenicity of casein hydrolysates prepared by papain

The effects of pH, temperature, enzyme-to-substrate ratio and reaction time on the antigenicity of casein hydrolysates were investigated. Response surface methodology (RSM) was employed to optimise the reaction conditions. Enzymatic hydrolysis with papain could reduce the antigenicity of α-casein and β-casein effectively and the reduction of antigenicity could be controlled by regulation of the reaction conditions. The model for optimal reaction conditions of a lower antigenicity of α-casein and β-casein was established. Under the range of conditions studied, enzyme-to-substrate ratio had the most significant effects on the antigenicity of α-casein and β-casein. The anti-α-casein IgG binding inhibition and anti-β-casein binding inhibition were both significantly negatively related with the degree of hydrolysis (DH).

Effects of Chitosan Coatings Enriched with Different Antioxidants on Preservation of Grass Carp (Ctenopharyngodon idellus) During Cold Storage

To investigate the effects of chitosan composite coatings for maintaining the quality of grass carp portions, indictors of microbiology (total bacteria count, TBC), chemistry (pH; total volatile basic nitrogen, TVB-N; 2-thiobarbituric acid, TBA; K-value), and sensory characteristics were analyzed periodically. The results showed that chitosan (1.5%, w/v) + acetic acid (1.0%, v/v) + tea polyphenol (TP, 0.5%, w/v) coating significantly (p ≤ 0.05) reduced growth of microorganisms as reflected in TBC, lipid oxidation as displayed in TBA, chemical spoilage as reflected in pH, TVB-N, K-value, and sensory characteristic scores compared to the control samples. The effect of chitosan (1.5%, w/v) + acetic acid (1.0%, v/v) + vitamin C (VC, 0.5%, w/v) coating was better than chitosan (1.5%, w/v) + acetic acid (1.0%, v/v) coating. Chitosan together with acetic acid and TP can be used as a type of preservative coating for grass carp portions under chilled storage.

Effects of Maillard reaction conditions on the functional properties of WPI chitosan oligosaccharide conjugates

Whey proteins are widely used as food material, but their functional properties are affected by processing conditions, in which Maillard reaction commonly occurs. The objective of this study was to investigate the effects of reaction conditions (saccharide rate (SR), setting time and setting temperature) on the functional properties of conjugates of whey protein isolates (WPI) - chitosan oligosaccharide (COS), which were produced by Maillard reaction. Response surface methodology (RSM) was used in this study, models for solubility, heat stability (HS), emulsifying activity (EA) and emulsifying stability (ES) of WPI-COS were established. Results indicated that the solubility of WPI-COS was 98.8xa0% at 29.8xa0% SR, 17.4xa0h, 46.7xa0°C; the heat stability of WPI-COS was 92.95xa0% at 27.2xa0% SR, 18.1xa0h, 48.7xa0°C; the EA of WPI-COS was 1.87 at 25.3xa0% SR, 20.0xa0h, 46.1xa0°C; the ES of WPI-COS was 13.28xa0min at 32.5xa0% SR, 12.0xa0h, 35.0xa0°C and setting temperature was the major factor affecting EA and ES while SR was the major factor affecting solubility and heat stability. Conditions were optimized for the preparation of WPI-COS to obtain improved functional properties.

Functional Properties of Water-soluble Proteins from Silver Carp (Hypophthalmichthys molitrix) Conjugated with Five Different Kinds of Sugar

Water-soluble proteins (WSP) from silver carp denature easily during thermal processing, leading to the reduction of functional properties. In order to improve the functional properties of WSP and to utilize its resources efficiently, five different kinds of sugars (i.e., xylose, glucose, galactose, oligo-isomaltose, and dextran-10) were used to conjugate with WSP by Maillard reaction. Results suggested that the use of the Maillard reaction improved the solubility, heat stability, and emulsifying properties of WSP. With the increase of molecular weight (MW) of the sugars, the solubility, emulsifying properties, and total sulfhydryl (SH) groups of WSP increased, while the surface hydrophobicity decreased. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the five Maillard reaction products (MRPs) showed that xylose reacted easily with WSP than did the other four kinds of sugar. Dextran-10 conjugated to WSP could efficiently improve the functional properties of WSP during heat processing.