INTRODUCTION

INTRODUCTION: Milk is a thick, white substance that contains numerous bene?cial components, and has, ever since, been a common household ingredient. According to studies, consumption of milk and milk products helps develop and maintain bones and teeth, reduces blood p r e s s u r e , s u p p o r t s n u m e r o u s m e t a b o l i c processes, boosts muscle mass and strength, and has even been found to assist in the production of the hormone serotonin, which when in low levels, is linked to depression (Ware, 2017). “Although milk from the cow is processed, it is not an engineered or fabricated food” (International Dairy Foods Association, n.d.). The two major types of milk being sold in the market is liquid milk and dried or powdered milk (Mishra, 2015).The main protein found in milk is casein, which is a phosphoprotein. This protein exists in milk as the calcium salt, calcium caseinate. It is composed of three similar proteins that primarily differ in their molecular weight and the amount of phosphorus groups attached to them. Namely, these are alpha-, beta-, and kappa-casein. Together, these three form a cluster called micelle, which is a lipid molecule. Casein, together with some fatty components that re?ect wide ranges of wavelengths, is responsible for the white color in milk (Mauk, 2013).C a l c i u m c a s e i n a t e h a s a n a p p r o x i m a t e isoelectric point of pH 4.6. Isoelectric point is the point at which a peptide or protein has a net charge of zero (Drabik, Mielczarek, Silberring, Smoluch, 2016). Thus, it is insoluble to solutions with a pH less than that of the given. Since milk has a pH of 6.6, the casein will have a negative charge and will be solubilized as a salt. When acid is added to the milk solution, the pH will be neutralized, and the neutral protein will precipitate. That is what happens when milk sours. The production of lactic acid lowers the pH of the milk, making the milk clot and form curds due to the precipitation of casein (Lawandi, 2015).DATA AND RESULTS:Before autoclaving, the isolated casein appeared to be a white-yellowish solid with a smooth texture. The ?ltrate was light yellow. After autoclaving, it turned into a dark brown solution with black precipitate. The explanation for this is that when casein reaches its isoelectric point, it has a pH where it is least soluble. As a result, precipitation occurs. Isolation and Hydrolysis of Casein from MilkChenille San Pedro, Gerardo Mari B. Sanchez, Shiela Singh, and Angeli M. Sta. Maria*Department of Psychology, University of Santo Tomas, EspaƱa, Manila, PhilippinesABSTRACT: Being the nearly perfect and most nutritious food that nature has to offer, milk is found to play a vital role in human nourishment. Casein, the basic protein in milk, was isolated from nonfat milk, through isoelectric precipitation. It was discovered that it was in its least soluble state when it was at its isoelectric point.

“Extraction of casein is usually carried out with membranes, ultra?ltration. Fat is the absolute enemy of these membranes and also you don’t need any fat in your casein extract. That’s why n o n – f a t m i l k i s u s e d f o r c a s e i n extraction.” (https://www.quora.com/Why-is-non-fat-milk-used-in-casein-extraction)EXPERIMENTAL:5g of powdered non-fat dry milk was placed in a 100mL beaker, and was dissolved in 20mL of warm distilled water. Once it reached 55 degrees Celsius, the beaker was removed from the hot plate. The initial pH of the milk solution was measured. Dropwise, a solution of 10% acetic acid was added to the milk solution while being stirred with a stirring rod. The number of drops was taken note of until the pH reached 4.6. The milk solution was left standing until a large amorphous mass was formed. The large amorphous mass was decanted. Using ?lter papers, the isolated casein was dried off. It was then weighed using an analytic balance, and its percent yield was determined. The isolated casein was divided into two portions: one for acid hydrolysis, and the other wrapped in aluminium foil to be stored in a refrigerator. The latter was later used to be characterised using various chemical tests.REFERENCES:https://www.medicalnewstoday.com/articles/273451.phphttps://books.google.com.ph/books?id=pY7wCgAAQBAJ&dq=Commercially+available+milk+can+be+classi?ed+into+two+major+groups:+liquid+milk+and+dried+or+powdered+milk.&source=gbs_navlinks_shttps://www.idfa.org/news-views/media-kits/milk/importance-of-milk-in-diethttps://www.livescience.com/32501-why-is-cows-milk-white.htmlhttps://www.sciencedirect.com/science/article/pii/B9780444636881000057https://www.thekitchn.com/the-science-behind-why-acid-curdles-milk-222962Table 1. Summary of resultsWeight of powdered non-fat dry milk5.1243gInitial pH6.10Final pH4.67No. of drops of 10% acetic acid used45 dropsWeight of crude casein3.3614gPercent yield65.60%Appearance before hydrolysisSmooth, white-yellowish solid in a turbid solutionAppearance after hydrolysisDark brown solution with black precipitate