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CHAPTER  ONE

INTRODUCTION

Background of the Study

Definition: Protein hydrolysate could be defined as the end product of protein hydrolysis using chemical and enzymic methods. Protein hydrolysate have many uses in specialty foods such as non allergenic infant formular, diets foods and other special nutritional foods. The drawback of many hydrolysates such as Soya or Casein hydrolysates is the bitter taste that develops when they are hydrolysated into small peptides with protease enzymes. Protein maldigestion which is often associated with cystic fibrosis and allergy to milk protein may be overcome by replacing intact in the diet with synthetic amino acid mixture, or with enzymic protein hydrolysates. Hydrolysates may be the treatment of choice for two reasons. The amino acids and small peptides constituents of protein hydrolysates have been shown to be more readily ascribed from the small intestine than their equivelent pure amino acid mixture, more over, protein hydrolysates are considerably less expensive than synthetic amino acid mixtures. Nonetheless, protein hydrolysates suffer from a serious drawback, namely, the occurrence of a bitter taste which develops during the course of the enzymic hydrolysis.

Murray r (1952) demonstrated that a treatment of enzymic casein hydrolysates with activated carbon resulted in a substantial improvement in the taste of preparations. However, authors regarded this method of improving the taste as impractical due to the simultaneous loss of a large proportion of the hyptophan during treatment. A different approach was presented in move recent studies in which a casein hydrolysate relatively free of bitter taste was obtained by the sequential employment of papa in and of pig’s kidney homogenate – the latter serving as a source of exopeptidases. However, extended time periods of hydrolysis were required, which necessitated the use of dolor form to control bacterial growth.

There is a variety of food and biomedical applications for protein which have been solubilized by enzymatic hydrolysis. Their enhanced solubility, heat stability, and resistance to precipitation in acidic environs, where many proteins are insoluble, offer attractive features to biochemists and nutritionists involve the research and development of high protein food formulations. Applications of these valuable protein supplements may have merit in the diet of persons with digestive disorders, pre and post operative abdominal surgical patient, geriatric and convalescent feeding , and for other who for various reasons do not ingest a well balanced diet. Unfortunately, the use of enzyme – treated hydrolysates in dietary food applications has in many instances, been limited due to the presence of bitter flovour component. The unpalatability of these hydrolysate  arises mainly from the formation of bitter peptide and amino acids liberated during the hydrolytic process. The bitterness appease to be closely related to the content and sequence of hydrophobic amino acids in the peptides.

Further hydrolysis of pepsin digested soy protein using a bacterial proteins or an exopeptidase, reduced bitterness. Also, chemotropic plastering protein hydrolysates. Similarly, clegg and Mc Millan (1974) have reported that a combination enzyme treatment of case in using papain for 18 hr followed by the addition of a homogenate of swine kidney cortex, also produced a hydrolysate with reduced bitterness. As another approach to resolving the bitter flavor problem, it seemed reasonable to attempt flavor improvement of protein hydrolysates by reducing the hydrophobic peptide and amino acid content of the digests. It was recognize many years earlier that activated carbon would absorb the aromatic  amino acids tryptophan, tyrosine, and phenycalaline. At a later date, Murrgy and Baker utilized carbon to treat a commercial enzymic hydrolysate of casein and reported the taste was greatly improved. A bitter tasting polypeptide fraction was elutated from the carbon.

Various phenol-formaldehyde resins with structures similar to carbon are available commercially and are used in a wide variety of ion-exchange and absorbent applications. Therefore the ability of a phenol-fomaldeliyde resin polymer to interact preferentially with the monoplane groups present in hydrophobic peptide was determined from the findings a hydrophobic chromatography process for debittering protein hydrolysates was developed. It has been well documented that the main problem in the preparation of soluble hydrolysate from protein such as casein is the difficulty in preventing the formation of bitter peptides or in removing them from the hydrolysate. Among several studies on casein hydrolysates the process developed by clegg and Mc Millan (1974) using skim milk as substrate, should be mentioned. By hydrolyzing skim milk protein with papain, a bitter testing hydrolysate is formed which is rendered bland by subsequent hydrolysis with exopeptidase from pig kidney tissue. Unfortunately, the procedure is both lengthy and costly. Anther costly debittering process involves hydrophobic chromatography of enzymatic protein hydrolysate on hexyls sepharose. An extraction method using azeotropic secondary butyl alcohol by which complete removal of bitter compounds is also achieved.

In the course of a study aimed a producing at a reasonable cost, bland, soluble skim milk hydrolysate without a significant loss of nutritional value, a comparison was made of adsorption methods of debittering pronase- and ficinhydroly-zed skim milks. The result of the comparison and the partial identification of the bitter peptides formed in the skim milk hydrolysates is reported. Due to the minimum changes in taste and appearance afforded to soft drinks or fruit juices by addition of this treated skim milk, the resultant beverages are expected to appear and taste like the original beverages with almost full nutritional value of skim milk. It is widely known that bitterness sometimes is produced in sake and other fermented products, so decreasing their qualities. This bitterness is produced by bitter peptides and their derivatives formed during the ageing process of these fermented products. Enzymatic hydrolysis of protein also produces bitter peptides very often to decrease the value of the products.

Since those bitter peptides are known to be produced by enzymatic hydrolysis, several attempts to reduce the production of bitter peptides during the enzymatic hydrolysis process by changing the enzymes and or conditions of the reactions have been made. Skim milk, soybean casein, whey protein concentrate (NPC) and casein hydrolysate of course composed of amino acids. Because a debittering method for bitter peptides was being looked for protein and peptides could block the bitterness. Creaming powder, Vegetable oil and margarine are fatly substances, which could block hydrophobic groups of bitter peptides by their character to reduce the bitterness. Some acidic amino acids were added in order to confirm their ability for masking bitterness, Asp, Glu and tau being used for the study. Although taurine (Tau) is not an acidic amin acid, it has a very strongly acidic function. Taurine was expected to reduce the bitterness as well as other acidic amino acids or peptides.

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