Influence of milk peptides in determining the functionality of milk proteins: a review

Production of whey protein hydrolyzates and its incorporation into milk

Abstract

Whey proteins provide an excellent source of low-molecular-weight bioactive peptides with important functional properties and bioactivities like antihypertensive, opioid, and antimicrobial effects. Presence of peptide molecules with lower molecular weight has a great role in food for health promotion. In this investigation, the release of low-molecular-weight peptides from whey protein concentrate was attempted by using enzymatic digestion. The hydrolyzate was then incorporated into milk to obtain enriched milk (EM) with low-molecular-weight peptides. Based on sensory analysis of EM, electrophoretic and RP-HPLC studies, hydrolyzates of 10% protein (degree of hydrolysis 5%; enzyme/ substrate E/S, 1:50) were finally incorporated into milk at 20% (v/v) to develop an acceptable product enriched with low-molecular-weight peptides. EM had higher protein content, viscosity and emulsifying properties than control milk with 3% fat. It is recommended that EM should not be sterilized as it results in coagulation, but can be safely pasteurized and spray dried without any undesirable effects. Maximum ACE-inhibition activity was obtained in hydrolyzate, followed by EM. This study is expected to boost the opportunity for the dairy industry to venture further into the nutraceutical dairy market.

Graphical abstract

Optimization of Bromelain-Aided Production of Angiotensin I-Converting Enzyme Inhibitory Hydrolysates from Stone Fish Using Response Surface Methodology

The stone fish is an under-utilized sea cucumber with many nutritional and ethno-medicinal values. This study aimed to establish the conditions for its optimum hydrolysis with bromelain to generate angiotensin I-converting enzyme (ACE)-inhibitory hydrolysates. Response surface methodology (RSM) based on a central composite design was used to model and optimize the degree of hydrolysis (DH) and ACE-inhibitory activity. Process conditions including pH (4-7), temperature (40-70 °C), enzyme/substrate (E/S) ratio (0.5%-2%) and time (30-360 min) were used. A pH of 7.0, temperature of 40 °C, E/S ratio of 2% and time of 240 min were determined using a response surface model as the optimum levels to obtain the maximum ACE-inhibitory activity of 84.26% at 44.59% degree of hydrolysis. Hence, RSM can serve as an effective approach in the design of experiments to improve the antihypertensive effect of stone fish hydrolysates, which can thus be used as a value-added ingredient for various applications in the functional foods industries.

Influence of degree of hydrolysis on functional properties and angiotensin I-converting enzyme-inhibitory activity of protein hydrolysates from cuttlefish (Sepia officinalis) by-products

BACKGROUND

In Tunisia the cuttlefish-processing industry generates large amounts of solid wastes. These wastes, which may represent 35% of the original material and constitute an important source of proteins, are discarded without any attempt at recovery. This paper describes some functional properties and the angiotensin I-converting enzyme (ACE)-inhibitory activity of protein hydrolysates prepared by hydrolysis of cuttlefish (Sepia officinalis) by-products with crude enzyme extract from Bacillus licheniformis NH1.

RESULTS

Cuttlefish by-product protein hydrolysates (CPHs) with different degrees of hydrolysis (DH 5, 10 and 13.5%) were prepared. All CPHs contained 750-790 g kg(-1) proteins. Solubility, emulsifying capacity and water-holding capacity increased while fat absorption and foaming capacity decreased with increasing DH. All hydrolysates showed greater fat absorption than the water-soluble fraction from undigested cuttlefish by-product proteins and casein. CPHs were also analysed for their ACE-inhibitory activity. CPH3 (DH 13.5%) displayed the highest ACE inhibition (79%), with an IC(50) value of 1 mg mL(-1).

CONCLUSION

Hydrolysis of cuttlefish by-product proteins with alkaline proteases from B. licheniformis resulted in a product with excellent solubility over a wide pH range and high ACE-inhibitory activity. This study suggests that CPHs could be utilised to develop functional foods for prevention of hypertension.

Structural and Functional Properties of Heat-processed Soybean Flour: Effect of Proteolytic Modification

Heat processing of soybeans alters its structural behavior, solubility, and in turn the functional properties. Heat-processed soy flour was prepared by autoclaving the defatted soy flour at 121 °C at 15 psi. The effect of enzymatic modification on the structural changes and functional properties of heat-processed soy flour was investigated. The combination of heat processing and enzymatic modification was carried out in two ways: (1) enzymatic modification followed by autoclaving and (2) autoclaving followed by enzymatic modification. Defatted soy flour (control), autoclaved soy flour, enzyme-modified flour, enzyme-modified and then autoclaved flour, autoclaved and then enzyme-modified flour were analyzed for physico-chemical and functional properties. Molecular weight profile of the protein was altered depending on the nature of treatments. Structural studies showed that enzymatic modification gave a porous type morphology to the particles. Enzymatic modification of autoclaved soy flour increased its surface hydrophobicity to 3136±400 units from 600±100 units of autoclaved soy flour. The results indicated that enzymatic modification of autoclaved soy flour increased its acid solubility (pH 4—4.5) from 17% to 56% over a control value of 24%. The foaming capacity of the enzyme-modified and then autoclaved soy flour was 80% while that of the autoclaved and then enzyme-modified flour was 42%. The soy flour that was autoclaved and then enzyme modified showed better emulsifying properties (174 mL oil/g flour) than the flour that was enzyme-modified and then autoclaved. The modified soy flour based on its functional and physico-chemical properties should find application in many food systems.

Properties of protein powders from arrowtooth flounder (Atheresthes stomias) and herring (Clupea harengus) byproducts

Functional, nutritional, and thermal properties of freeze-dried protein powders (FPP) from whole herring (WHP), herring body (HBP), herring head (HHP), herring gonad (HGP), and arrowtooth flounder fillets (AFP) were evaluated. The FPP samples have desirable nutritional and functional properties and contained 63-81.4% protein. All FPP samples had desirable essential amino acid profiles and mineral contents. The emulsifying and fat adsorption capacities of all FPP samples were higher than those of soy protein concentrate. The emulsifying stability of WHP was lower than that of egg albumin but greater than that of soy protein concentrate. Thermal stability of the FPP samples is in the following order: HGP > HBP > WHP > HHP > AFP.

Heat-induced destabilization of oil-in-water emulsions formed from hydrolyzed whey protein

The emulsifying ability, heat stability, and coalescence stability of oil-in-water emulsions prepared with whey protein of varied degrees of hydrolysis (DH), and at varied protein contents, was studied. Whey protein hydrolysates (WPH) with a DH of 4% and 10% had poorer emulsifying ability than non-hydrolyzed whey protein concentrate (WPC), but were more heat stable. Increasing DH between 10 and 27% improved emulsifying ability and further improved the heat stability of the emulsion droplets. Increasing DH from 27 to 35% led to a big decrease in both emulsifying ability and heat stability. The quiescent coalescence stability of WPH emulsions was relatively good up to a DH of 27%. Above DH 27% emulsions become highly unstable. It appears that two mechanisms of instability are at work here. At low DH heat-induced denaturation and aggregation occur. In the DH range of 4-20% heat stability increases as protein globular structure is disrupted. At a DH greater than 27% we see a change from a hydrolysis-induced increase in heat-stability to coalescence instability, with a resultant large increase in emulsion breakdown during heating.

Effects of various whey protein hydrolysates on the emulsifying and surface properties of hydrolysed lecithin

Oil-in-water emulsions (30 wt% sunflower oil) containing various concentrations of commercial whey protein hydrolysates (0-4 wt%) and hydrolysed lecithin (0.4-1.8 wt%) were prepared by means of a high pressure homogeniser. The degrees of hydrolysis used ranged from 10 to 27%. The individual and interactive effects of these factors on the particle size distribution, emulsion stability, consistency and interfacial tension were investigated using a three-level factorial design according to the principle of response surface methodology. The properties of the emulsions containing both hydrolysed lecithin and whey protein hydrolysate (WPH) were significantly influenced by the degree of hydrolysis of WPH, the protein content and the second-order interaction between both. Addition of WPH, with a 10-20% degree of hydrolysis, improved the stability of lecithin-stabilised emulsions and slightly decreased the average droplet size, compared to those emulsions with only protein or hydrolysed lecithin. However, when extensively hydrolysed WPH (DH=27%) was mixed with hydrolysed lecithin, rapid coalescence and oiling-off of the emulsion droplets resulted, suggesting competition between the surface active components of this WPH and the hydrolysed lecithin. High amounts of such an extensively hydrolysed WPH, together with low lecithin concentrations, were found to be especially detrimental. The different behaviour of partially and extensively hydrolysed WPH in oil-in-water emulsions containing hydrolysed lecithin, was in good agreement with their interfacial activity, as measured by the drop volume method.

Behaviour of formula emulsions containing hydrolysed whey protein and various lecithins

Formula emulsion systems are used as enteral, sports and health products. In some formulas addition of hydrolysed protein is necessary to guarantee ease of digestion and hypoallergenicity. In the low fat emulsion model an increase in the content of lecithin (phospholipid mixture) was required, in consideration of the advice of the Food and Nutrition Board (USA) for choline supplementation. The individual and interactive effects of whey protein isolate (WPI) or hydrolysate (WPH) (3.7 and 4.9% w/w), unmodified deoiled or hydrolysed lecithin (0.48 or 0.7% w/w) and carbohydrate in the form of maltodextrin with dextrose equivalent (DE) 18.5 or glucose syrup with DE 34 (11% w/w) on the properties of formula emulsions with 4% v/w sunflower oil, were investigated using a full factorial design. The emulsions were characterised by particle size distribution, coalescence stability, creaming rate, and also surface protein and lecithin concentration. WPI-containing emulsions proved to be stable against coalescence and showed only little creaming after 1 and 7 days standing. There was a significant increase in the mean droplet size and a significant deterioration of coalescence and creaming stability when WPH instead of WPI was used as the protein source, due to the lower number of large peptides and lower surface activity of the WPH. Increasing the WPH concentration led to an increase in oil droplet size and further deterioration of the stability of the emulsions. The starch hydrolysate and lecithin also significantly influenced the emulsion properties. Their influence was less strong when the emulsion contained WPI. Under the conditions used WPH-based emulsions were more stable, in terms of creaming and coalescence, when a low level of protein was used in conjunction with hydrolysed lecithin and glucose syrup. Oil droplets in emulsions containing unmodified lecithin in either the continuous or disperse phase and WPH in the continuous phase were very sensitive to coalescence. The addition of starch hydrolysates (DE 18.5) induced intensive flocculation and phase separation in these emulsions.

Milk protein-derived opioid receptor ligands

Milk is mammalian characteristic and is of particular importance for humans: Mother's milk or its substitutes from cows' milk are absolutely essential nutriments for the neonate and cows' milk also represents a basic foodstuff for adults. However, in addition to their well-known nutritive role, milk constituents apparently are also able to carry specific information from the milk producer's to the milk receiver's organism: Thus, a number of milk protein fragments has been shown to behave like opioid receptor ligands able to address opioidergic systems in the adult's or in the neonate's organism. With respect to the proteins, which they are derived off these peptides have been named alpha-casein exorphins or casoxin D (alpha-casein), beta-casomorphins or beta-casorphin (beta-casein), casoxin or casoxin A, B, or C (k-casein), alpha-lactorphins (alpha-lactalbumin), beta-lactorphin (beta-lactoglobulin) or lactoferroxins (lactoferrin). Only casoxins and lactoferroxins display antagonistic properties; the other peptides behave like opioid receptor agonists. Most of the information available so far has been collected about beta-casomorphins. These peptides obviously can be released from beta-casein in the adult's or in the neonate's organism, where they might elicit opioid effects in the frame of a regulatory role as "food hormones". Several synthetic beta-casomorphin derivatives have been shown to be highly specific and potent mu-type opioid receptor ligands which frequently have been used as standard tools in opioid research.

Biochemical and functional properties of Atlantic salmon (Salmo salar) muscle proteins hydrolyzed with various alkaline proteases

Protein hydrolysates (5, 10, and 15% degrees of hydrolysis) were made from minced salmon muscle treated with one of four alkaline proteases (Alcalase 2.4L, Flavourzyme 1000L, Corolase PN-L, and Corolase 7089) or endogenous digestive proteases. Reaction conditions were controlled at pH 7.5, 40 degrees C, and 7.5% protein content, and enzymes were added on the basis of standardized activity units (Azocoll units). Proteases were heat inactivated, insoluble and unhydrolyzed material was centrifuged out, and soluble protein fractions were recovered and lyophilized. Substrate specificities for the proteases was clearly different. Protein content for the hydrolysates ranged from 71.7 to 88.4%, and lipid content was very low. Nitrogen recovery ranged from 40.6 to 79.9%. The nitrogen solubility index was comparable to that of egg albumin and ranged from 92.4 to 99.7%. Solubility was high over a wide range of pH. The water-holding capacity of fish protein hydrolysates added at 1.5% in a model food system of frozen minced salmon patties was tested. Drip loss was on average lower for the fish protein hydrolysates than for egg albumin and soy protein concentrate, especially for Alcalase hydrolysates. Emulsification capacity for fish protein hydrolysates ranged quite a bit (75-299 mL of oil emulsified per 200 mg of protein), and some were better than soy protein concentrate (180 mL of oil emulsified per 200 mg of protein), but egg albumin had the highest emulsifying capacity (417 mL of oil emulsified per 200 mg of protein). Emulsification stability for fish protein hydrolysates (50-70%) was similar to or lower than those of egg albumin (73%) or soy protein concentrate (68%). Fat absorption was greater for 5 and 10% degrees of hydrolysis fish protein hydrolysates (3.22-5.90 mL of oil/g of protein) than for 15% hydrolysates, and all had greater fat absorption than egg albumin (2. 36 mL of oil/g of protein) or soy protein concentrate (2.90 mL of oil/g of protein).

Effect of pH during heat processing of partially hydrolyzed whey protein

Whey protein isolate was modified by proteolysis using a broad-spectrum protease in combination with heat treatment of the hydrolysate. Half of the beta-lactoglobulin content was hydrolyzed when the degree of hydrolysis reached 5.1%. alpha-Lactalbumin and BSA were not attacked by the enzyme. Heating of the hydrolysate resulted in the formation of small and large aggregates, the proportion of which depended on the degree of hydrolysis and the pH during heating. The decrease in total sulfhydryl groups, as the degree of hydrolysis and heating pH increased, was associated with the formation of disulfide bonds. Whey protein hydrolysis at a degree of hydrolysis of 1.7%, followed by heating at pH 8.0, resulted in the highest amount of accessible sulfhydryl groups, reflecting the unfolded structure of the aggregates. Hydrolysate solubility at neutral pH averaged 98% when pH during heating was 4.0 or 8.0. Heating of whey protein at pH 6.0 resulted in a much lower solubility, which was attributed to the high proportion of large aggregates. Solubility of the hydrolysate at pH 4.5 was higher when pH during heating was adjusted to 4.0. Solubility of the hydrolysate heated at pH 6.0 and 8.0 improved with degree of hydrolysis > 1.7%. Results are discussed in relation to interactions of proteins and peptides during heat processing.