Food Analysis

How to Prepare store and preserve the Lab Samples for Food Analysis in 3 Min – Learn easy

08/11/2021

by Vijay Gladwin with No Comment Food Technology

know in detail about the preparation storage and preservation of laboratory samples for food analysis is explained

Preparation of Samples for Food Analysis

The preparation of the samples for food analysis involves reducing the amount and simultaneous reduction in particle size by thorough mixing.

To obtain precise analytical results, the laboratory samples for food analysis must be made as homogeneous as possible so that the results are reproducible within the limits of the analytical method used.

The method of homogenisation will depend on the type of food being analysed. Usually, the samples for food analysis are abstracted from different portions of the food material, mixed and blended, and the representative sample is taken.

A number of very effective electrical, mechanical devices are available to slash the size of food particles and to mix food products thoroughly, mincers, graters, blenders and homogenisers for dry, moist, and wet foods, and several types of powder mills or grinders are all essential pieces of equipment.

Mechanical devices produce heat, so care must be taken not to alter the sample’s composition by losing moisture due to overrunning the equipment.

Coning and Quartering for sample preparation

Dry foods

Pulses and cereals

The sample for food analysis is cleaned free of sand, stone and other extraneous material and powdered. The size of powdery food can be reduced by a process called Quartering.

samples for food analysis — Pulses and cereals

Flesh foods

Either the whole tissue or a representative protein is minced and then blended with double its weight of water. Portions of the slurry are then removed into weighed containers which are then reweighed to determine the amount of tissue used.

Fluid foods

The top or bottom-drive blenders best emulsify the sample for food analysis.

Oils and fats

They are prepared by gentle warning and mixing. Faty mixed-phase products such as cheese, butter, margarine and chocolate are challenging to be prepared by gentle warming and mixing. Cheese and chocolate are best grated, followed by hand mixing of grated material. Butter and margarine may be re-emulsified by blending by hand in a glass jar after warming to 35ºC to melt the fat.

Fruits and vegetables

The samples for food analysis are taken small in size. However, big ones should be cut, and portions of the edible material should be used. The non-edible portions are rejected, and the edible portions are cut into small pieces. Samples are taken from the mixture of these pieces by Quartering. It is preferable to use stainless steel trays, knives and scissors for preparing the sample.

Prepared samples for food analysis may change composition through evaporation or absorption of moisture or by the action of enzymes or microorganisms. The components which are likely to change should be analysed immediately after preparation.

Preservation of samples for food analysis

The prepared samples for food analysis are stored in hermetically sealed inert containers like glass jars or wide-mouthed bottles with screw caps or friction top tin containers.

The dried fruits and fruit products containing 20-30% moisture are stored in glass or plastic containers.

Hydrolytic changes caused by the enzymes may be prevented by dropping the sample into boiling alcohol. The alcoholic extracts are stored below 0ºC to avoid changes in composition.

Products likely to undergo microbial spoilage may be preserved using acetic acid or sodium benzoate as a preservative by freezing or drying.

Freezing of samples for food analysis

Freezing of samples for food analysis in air and moisture-proof containers by rapid freezing and storage at less than -6ºC prevents microbial activity, but not enzyme activity, which continues to occur although at a slower rate temperature down to -40ºC.

Storage of dried products at 0ºC to 10ºC minimises deterioration. While taking samples stored at low temperature for analysis, either the entire sealed container should be warmed to room temperature or a portion transferred quickly to a clean, dry stoppered container to avoid changes in moisture content.

Moisture

Water in plant foods may occur in any of three different forms

As a dispersing medium for the colloids and as a solvent for crystalloids, i.e. as free water.
It may be absorbed on the surfaces of colloidal particles in the protoplasm, the cell walls, and cell constituents such as proteins, starches, cellulose which hold water tenaciously.
As the water of hydration in chemical combination, with various substances like carbohydrates and hydrates of salts.

The “bound water” found in biological materials and the water in colloidal systems may exist as

Occluded water
Capillary water
Osmotic water
Colloidal water bound by physical forces
Chemically bound water

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Easy to Learn about Food analysis in 3 Min

07/11/2021

by Vijay Gladwin with No Comment Food Technology

know in detail about food analysis procedures and their techniques

Food analysis is concerned with the development of criteria of quality and identity, with techniques suitable for use in the laboratory.

In earlier times, the food analyst was mainly concerned with gross adulteration. Nowadays, since there is an increasing tendency to manufacture foods about market requirements, processed foods, and fast foods are fast developing.

The food analysis is done with one or more of the three different objectives.

Developing safe foodstuffs with consumer acceptance.
The legal point of view for the sake of prosecution
From the research point of view in educational institutions and research organisations

Processed foods are produced within the units of prescribed manufacturing standards, also set to comply with legal or other recognised requirements.

This is attained by standardising as far as possible, the process at each stage, from the farm to the dining table. This has resulted in the development of analytical techniques which are suitable for rapid assessments and control.

Earlier methods are about subjective criteria like flavour, texture, colour, and other qualities were preferred. However, now methods that give quick, reproducible, accurate and objective procedures are replacing the subjective methods for the evaluation of food quality.

Many of the food analysis procedures have been empirically developed with special reference to the particular food product. Such methods are precise or reproducible. Most of these procedures also yield accurate results.

The procedure is given for the analysis of a particular compound need not be applicable for a similar compound. In many food laboratories, most of the routine work comprises methods of proximate analysis and the study of colour additives and contaminants.

The main compositional components of interest are moisture, fat, protein, ash available and unavailable carbohydrates. The moisture value obtained by drying methods may include other volatile matter such as essential oils, traces of volatile acids and amines.

The preparation of the samples plays a vital role in food analysis. Sugars from natural sources such as fruits are conveniently expressed as total soluble solids as measured by refractometric determination.

Protein can be calculated from the total nitrogen as determined by Kjeldahl’s method. In many estimations, allowance has to be made for interference arising from the food itself or contamination of the reagents, and blank determination must be performed. Allowance may sometimes have been made for changes that occur during storage.

Internationally recognised reference procedures have been published by bodies such as ISO, IUPAC, Codex Alimentarius and the AOZC in the UK, the British standards institution and the analytical division of the chemical society.

As in other fields of analysis, the availability of suitable methods is essential if accurate results are to be obtained. Good results depend on the choice of the experiment, the analytical procedures used and the accurate determination and interpretation of the results.

The food analyst should be acquainted with the theory of each estimation and should strive for accuracy. With the available equipment, the food analyst decides on the feasible methods to be used in the laboratory.

Sampling – Food Analysis

The perfect sample is 100% of the food material being analysed. This is possible only when the quantity of the food to be analysed is small enough.

For a high quantity of food, a representative sample is usually obtained. When the food particle is homogeneous, a sample can be taken.

However, when the food is heterogeneous, the problem of getting a sample is difficult. Hence the food analyst should be familiar with the sampling procedures.

The value of the result of chemical analysis on a well-prepared laboratory sample depends on how representative of the sample is of the lot, batch, package, or consignment of the particular food from which it was taken and on the kind of chemical information that is required.

Foodstuffs and food ingredients are relatively heterogeneous materials, so it is difficult to obtain a single representative sample for sample analysis.

The problem may be minimised by selecting, either randomly or according to a plan several samples from the lot. These samples may be analysed separately to yield results from which the average composition of the lot may be computed.

In some instances, the samples may be thoroughly mixed to give a single large representative bulk sample from which a sample may be taken for laboratory analysis.

The process of sampling is one facet of statistics, and most books on statistics include chapters describing the elementary mathematical principles involved.

There are ISO standards for the sampling of various foodstuffs. Because of the practical difficulties and economic aspects of full statistical sampling, and the natural variation in the composition of foodstuffs, food analysis is often out randomly chosen single samples.