BS ISO 13082 pdf download

BS ISO 13082 pdf download Milk and milk products — Determination of the lipase activity of pregastric lipase preparation
1 Scope
This International Standard specifies a method for the determination of the lipase activity. lt is intended for thepreparation of pregastric lipase and rennet paste, both of animal origin.
NOTE No reference method was used to check this method as no stable standard can be found. On the other hand,a reference method can be omitted as the substrate is reproducible and well defined.
2Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
international lipase unitILU
amount of lipase activity that releases butanoic acid, also known as butyric acid, at a rate of 1.25 umolminunder specified conditions
NOTE 1 Lipase activity is expressed either in international lipase units (ILU) per gram of product or lLU per millire ofproduct.
NOTE2 The definition is based on the direct consumption of titrant while not considering that a small molar fraction ofthe butyric acid (4 %) is not dissociated and thus cannot be titrated.As such, that creates a small error in the definition.
3Principle
Triglyceride esters are hydrolysed by lipase. The free fatty acids (as butyric acid) released from the substratetributyrin are titrated in a pH-stat with sodium hydroxide.The amount of sodium hydroxide consumed within adefined period is used to calculate the activity in lLU per millilitre or lLU per gram.
Due to the non-existence of a reference standard,it is recommended that a control (known) sample beincluded in the test.
4Reagents
During the analysis,unless otherwise stated, use only reagents of recognized analytical grade and distilledwater or demineralized water or water of equivalent purity.
The brand of chemicals can affect the result. Therefore, before using a brand other than the one mentioned,verify whether it gives the same result.
4.1 Tributyrin (glycerintributyrate or glyceryl tributyrate), e.g. Merck No. 1.01958.0100 1 ) or similar.
4.2 Sodium caseinate, e.g. Sigma C8654 1) or similar.
4.3 Lecithin, from soya bean, e.g. BDH Prod. 29863 1) or similar.
4.4 Liquid paraffin. Use paraffin which is highly liquid (or similar light mineral oil), e.g. Merck No. 7174.1000 1) , or similar.
4.5 Soda lime granules [Carbosorb 1) ], e.g, BDH no 331104 1) or similar.
4.6 Sodium hydroxide solution, c(NaOH) 0,025 mol/l, which can either be purchased or be prepared as follows.
Using a pipette (5.1), add 25,00 ml of 1 mol/l sodium hydroxide with an accurately known titre into a container.
Dilute with water to 1 000 ml.
The 0,025 mol/l NaOH solution can be kept in a closed container, protected against carbon dioxide in the air by use of a CO 2 trap with soda lime (4.5) at room temperature for at least 1 month. If necessary, seek advice from the supplier of the equipment or reagent. Change the soda lime at least once a year.