Why we use Boric Acid only in Protein Estimation by Kjeldahl Method???

Ammonia which is liberated during steam distillation of digested protein sample is soluble in boric acid as well as it is sparingly soluble in water.

Suppose, we use water instead of boric acid, then the chemical reaction will be,

NH₃ (g) + H₂O (aq) -----> NH₄⁺ + OH^-

which is a basic solution and it is not a complex to give any indicator reaction. Also, solubility of ammonia in water is temperature dependent so any minute variation of temperature can result in loss of captured ammonia.

Boric acid (H₃BO₃ or HBO₂.H₂O) is added (in excess) to form a stable and soluble complex with the steam-distilled ammonia gas:

NH₃ (g) + HBO₂.H₂O (aq) -----> NH₃.HBO₂ (aq) + H₂O

which then can be titrated directly with 0.05 M sulphuric acid till pH = 5.

2 NH₃.HBO₂ (aq) + H₂SO₄ (aq) ----->              2 NH₄⁺ + HBO₂.H₂O (aq) + SO₄^2-

This titration gives colour change for quantitative analysis of protein.

Note: Boric acid (HBO₂.H₂O) is a very weak acid pKa=9.3 and is not interfering with the acid/base titration of ammonia.

Can L-sugars be used instead of artificial sweetners???

Depending upon how the sugar molecule is organized, it can be what is called, left or right handed. They will have exactly the same elements in exactly the same ratios, but be oriented differently. A levo or L-sugar is a left-handed version of the molecule. A Dextro or D-sugar is the right-handed version; Levo, from the Latin for Left and Dextro, from the Latin for Right. It refers to the properties of rotating plane polarized light. If the light rotates clockwise as it approaches an observer, this is known as dextrorotation, light with a rotation to the right. If the light rotates counterclockwise as it approaches the observer, then the light exhibits levorotation, rotation to the left.

Levo-sugar is a confusing chemical to the human body. To the tongue, it tastes just like regular sugar. But the body has never swallowed left- handed sugar and can't digest it.

e. g. L-Glucose does not occur naturally in higher living organisms, but can be synthesized in the laboratory. L-Glucose is indistinguishable in taste from D-glucose, but cannot be used by living organisms as source of energy because it cannot be phosphorylated by hexokinase, the first enzyme in the glycolysis pathway. 

One of the known exceptions is in Burkholderia caryophylli, the enzyme D-threo-aldose dehydrogenase is capable of oxidising L-glucose. L-Glucose was once proposed as a low-calorie sweetener and it is suitable for patients with diabetes mellitus, but it was never marketed due to excessive manufacturing costs.  The acetate derivative of L-glucose, L-glucose pentaacetate, was found to stimulate insulin release, and might therefore be of therapeutic value for type 2 diabetes. L-Glucose was also found to be a laxative, and has been proposed as a colon-cleansing agent which would not produce the disruption of fluid and electrolyte levels associated with the significant liquid quantities of bad-tasting osmotic laxatives conventionally used in preparation for colonoscopy.

So, in today’s world, after various side effects of artificial sweeteners in long term consumption, L-sugars can be again part of food scientist’s subject for discussion.

 Video on Carbohydrate Digestion in Human Body...

Different Enzymes and their Applications in Food Industry

Enzymes are nothing but proteins but play a very important role in very minute concentrations. They are just like 'Wonder Chemicals' for preparation of various food products. They have wide array of use in industries like Food, textile, paper, biotechnology etc....  Some of the major enzymes used in food industry are given here with their applications-

1.      Alpha-amylase: Converts starch to dextrin in producing corn syrup. Solubilizes carbohydrates found in barley and other cereals used in brewing.

2.      Gluco-amylase: Conversion of dextrin to glucose in the production of corn syrup. Conversion of residual dextrins to fermentable sugar in brewing for the production of "light" beer.

3.      Beta-glucanase: Breakdown of glucans in malt and other materials to aid in filtration after mashing in brewing.

4.      Lipase: Enhancing flavour development and shortening the time for cheese ripening. Production of specialty fats with improved qualities. Production of enzyme-modified cheese/butter from cheese curd or butterfat.

5.      Papain: Used as meat tenderizer. Used in brewing to prevent chill-haze formation by digesting proteins that otherwise react with tannins to form insoluble colloids.

6.      Chymosin: Curdling of milk by breaking down kappa-caseins in cheese making.

7.      Microbial proteases: Processing of raw plant and animal protein. Production of fish meals, meat extracts, texturized proteins, and meat extenders.

8.      Pectinase: Treatment of fruit pulp to facilitate juice extraction and for clarification and filtration of fruit juice.

9.      Lactase: Additive for dairy products for individuals lacking lactase. Breakdown of lactose in whey products for manufacturing polyactide.

10.  Acetolactate decarboxylase: Reduction of maturation time in wine making by converting acetolactate to acetoin.

11.  Glucose oxidase: Conversion of glucose to gluconic acid to prevent Maillard reaction in products caused by high heat used in dehydration.

12.  Cellulase: Conversion of cellulose waste to fermentable feedstock for ethanol or single-cell protein production. Degradation of cell walls of grains, allowing better extraction of cell contents and release of nutrients.

13.  Zymase: It is an enzyme complex that catalyses the fermentation of sugar into ethanol and carbon dioxide. It occurs naturally yeasts.

14.  Protease: Used for breakdown of protein into constituent amino acids. Biscuit manufacturers use them to lower the protein level of flour.

15.  Trypsin: It is one of the types of protease enzyme. Mainly used to predigest baby foods.

16.  Renin: It is derived from stomach of young ruminant animals (like calves and lambs). It is used in the manufacture of cheese, mainly used to hydrolyse protein.

Reference: "Food Enzymes: Structure and Mechanism". DWS Wong. 1995.