eChapters

Theory

The specific gravity is defined as the unit weight of the product mass divided by the unit weight of distilled water at 4°C. The unit density is obtained by measuring the volume and weight of a unit product. Sometimes it is required to compare the density of the product to the density of water. This comparison is in the form of ratio and is termed as the specific gravity.

Specific gravity also known as relative density is the ratio of density of a substance to the density of a standard substance at the same temperature and pressure. For solids and liquids the standard substance is water while for gasses it is air. The specific gravity of food material play an important role in design of storage bins, conveying equipments, separation equipments, etc. The specific gravity is frequently used to solve the various phase relationships, including void ratio, porosity and degree of saturation together with the moisture content and unit weight. It is also used in calculations associated with the grain size analysis, consolidation and compaction. Pycnometer method, which is a standardized vessel for determining specific gravity. It involves a standard container of accurately defined volume used to determine the specific gravity of solids and liquids.

Determination of Specific Gravity

The palatability of the citrus fruit is associated with its internal quality. Measuring specific gravity provide clues to internal quality of the fruit. The ratio of the weight of the fruit to its submerged weight indicates specific gravity. Specific gravity also indicates relationship between fruit weight and volume.

Steps: To determining specific gravity

Record the weight of fruit in air on top loading balance.

Materials Required

Specific gravity bottles, weighing balance, sample, pipettes, thermometer, distilled water 

Procedure

    1.    Take the sample and distilled water record their temperatures (they should be same for correct estimation). If the temperatures are not same bring both to 20ºC or the room temperature.
    2.    Clean and dry the specific gravity bottles properly before use.
    3.    Record the tare weight of the specific gravity bottle (T) alongwith the stopper.
    4.    Carefully fill the specific gravity bottle with distilled water up to the brim and then place the stopper tightly so as to exclude extra water. 
    5.    Dry the exteriors of the bottle with a tissue paper
    6.    Record the weight of (bottle + water) say A
    7.    Similarly, fill the same specific gravity bottle with test sample and record the weight (bottle + sample) say B
    8.    Calculate the specific gravity of solution using the following formula

Theory

Specific heat is defined as the amount of heat needed to raise the temperature of one kg of the material by one degree at constant pressure without a change in state. With food materials, specific heat is a function of different components of a food, moisture content, temperature, and pressure. Specific heat is an important parameter in thermal analysis of food processing and equipment used in heating or cooling of foods. The numerical values of specific heat of the food materials are used in designing food processes and processing equipment. It can be used to calculate the heat load imposed on the refrigeration equipment by the freezing of foods. An apparent specific heat is used in freezing or thawing and in most food processing applications.

The specific heat of a food increases as the product moisture content increases. In unfrozen foods, specific heat capacity is relatively constant with respect to temperature. However, for frozen foods, there is a large decrease in specific heat capacity as the temperature decreases. The specific heat of a material can be determined experimentally by static (adiabatic) calorimetry or differential scanning calorimetry. It can be also predicted quite accurately with the help of a number of empirical equations. The equations are empirical expressions, obtained by fitting experimental data into mathematical models. The mathematical models are based on one or more constituents of the food. Since water is a major component of many foods, a number of models are expressed as a function of water content.

Stomata are pores formed between two specialized epidermal cells, the guard cells, which are found on the surface of aerial parts of higher plants (leaves). They control the gas exchange between the leaf and the ambient air. Their main functions is to facilitate the entry of CO² into the leaf for photosynthesis and loss of water vapour for evaporative cooling of the leaves.

The guard cells are formed by the transverse division of stomatal mother cells that differ morphologically and biochemically from other epidermal cells. The middle lamella disintegrates and the two walls separate leaving an opening between them the stomatal pore. The walls bordering the pore become considerably thickened. They are generally cutinised. This radial thickening of the inner wall plays an important role in stomatal movement. Stomata control 95 per cent or more of CO² and water vapour exchange between the leaf and atmosphere.

Location and occurrence of stomata: Stomata are found in all higher plants down to the evolutionary level of the phylum Bryophyta. Stomata are not found in liverworts. In the leaves of most herbaceous plants the stomata are found in both upper (Adaxial) and the lower (Abaxial) surfaces. Such leaves are known as Amphistomatus. Usually in tree species, stomata are found only on the lower surface of the leaves. Such leaves are called Hypostomatus. Aquatic plants with floating leaves such as water lilies have stomata only on the upper surface and such leaves are called Epistomatus. Most of submerged aquatic plants do not posses stomata and diffusion of gases occurs between water and plant tissues across a thin cuticle. In many cases subsidiary cells are present adjacent to the guard cells. These are specialized epidermal cells which are usually different in size and shape from other epidermal cells. They are usually smaller than the epidermal cells and have more dense cytoplasmic contents and a greater frequency of cell organelles. In grasses and some other species, subsidiary cells are intimately involved in stomatal mechanism.

Diffusion of gases through stomata is governed by the two important parameters associated with the stomata, viz., the stomatal frequency and the extent of opening of the stomata. Stomatal frequency is defined as the number of stomata per unit leaf area (no.mm ^-2 ). Apart from the stomatal frequency, yet another parameter that reflects the stomatal distribution is the stomatal Index. It is the ratio of the number of stomata per unit leaf area to the total number of epidermal cells and is generally expressed in percentage.

(Method of Bryant et al., 1959)

Strontium and barium are adsorbed on a cation-resin column, and  after a suitable gowth period, yttrium-90, the daughter of strontium-90, is selectively eluted. The yttrium-90 is then adsorbed on and eluted from a second cation-resin column and counted. The radiochemical yield is greater than 97% gravimetric measurement of the recovery of strontium and yttrium carriers is not required. The method, with modifications, is applicable to samples that contain 100 mg of iron or uranium.

Principle: The copper in the Fehling solution is reduced to red, insoluble cuprous oxide in the presence of invert sugars like glucose and fructose. The quantity of sugars solution liquids for complete neutralization of a known quantity of Fehling mixture is determined by titration using methylene blue as the indicator.

(Lane and Eynon Method)

6.25 HNO3 (for 2 ltr) : Take 181 ml of conc HNO3 and diluted to 2 ltr in a volumetric flask.

Aim

To determine the tapped bulk density and flowability of the food powder.

Materials required

Raw material (powder)

Measuring cylinder

Electronic weighing balance

Tapped bulk density of the powder

Tapped bulk density is measured for powdery samples. The volume is measured after tapping the powdery material so that the product is adjusted to inter-granular spaces, but it cannot eliminate all the inter-granular spaces. The tapped density is an increased bulk density attained after mechanically tapping a container containing the powder sample.

Theory

Texture testing is a well-established technique for evaluating the mechanical properties of raw materials, food structure, pre- and post- harvest quality control checks. The texture testing has many applications across wide range of foods including cereals, fruits, vegetables, meat, poultry, fish, baked foods, confectionaries, snacks, dairy, gelatins, pasta, etc. Food texture analysis of foods can highlight the quality improvement throughout the supply chain. At research and development stage, new or alternative ingredients can be compared with existing ingredients.

Texture profile parameters

The texture profile parameters including hardness, firmness, crispiness, rupture strength springiness, chewiness, cohesiveness, gumminess, gel strength, adhesiveness, consistency, crunchiness, elasticity, extensibility, fracturability, stiffness, stringiness, toughness, work to cut, penetrate and shear can be measured by the mechanical food texture analyzer.

Aim

To determine the reduced level of various points

To find out difference of elevations of two points

Materials required

Dumpy level

Levelling staff

Field capacity may be defined as the amount of water held in soil after excess water has drained away and the rate of downward movement of water was materially decreased which usually taken place within two to three days after heavy rain or irrigation. In this condition water was moved out of the macropores and air has moved into take its place. 

Infiltration is the entry of a fluid from one medium into another. Soil water plays an important role in nature. The entry of rain or irrigation water into soil is called infiltration. Infiltration rate is defined as the amount of water entering into a soil per unit area per unit time under one atmospheric pressure. The infiltration rate depends upon initial moisture content of soil, condition of soil surface and permeability of various layers.

The maximum water holding capacity is the amount of water, expressed as percentage on oven dry basis held by a soil when it is completely saturated with water. At this moisture content, all the pore spaces are completely filled with water.

Object: Determination of the viability of seeds by tetrazolium test. 

Material required: Healthy seeds, tetrazolium solutions, beakers, water and petridishes. 

Theory: Viability of seeds shows their potential towards germination.

Aim

To determine the thermal conductivity of the agricultural materials probe method.

Materials required

Thermal conductivity probe

Stainless-steel sample container

Grain or powder sample

Graph sheet

Power source

Materials Required

Sample, 0.1 N NaOH solution, 1% phenolphthalein indicator solution, beakers, conical flasks, pestle and mortar, funnels, volumetric flasks, pipettes, pH meter, shaker.

Reagents

    1.    0.1 N NaOH: Dissolve 4 g NaOH (AR) crystals in sufficient water to make up the final vol. 1 litre.

    2.    1 % Phenolphthalein: Dissolve 1 g in 100 ml water. Readymade indicator solutions are more commonly used.  

Procedure

Preparation of sample: For fresh fruits and vegetables, prepare a well blended, uniform pulp in a pestle and mortar and for processed products, take out a representative sample and blend it well so that it becomes uniformly soluble when added to water. Filter through a fine muslin cloth or coarse filter paper if felt necessary. The liquid samples can be taken directly for estimation.
    1.    Take out a known weight / vol. (say 20 g) of sample in a beaker (in 3 replicates).
    2.    Make it to a known vol. (say 100 ml) with added distilled water.
    3.    Take 10 ml of this aliquot in a conical flask.
    4.    Add 1-2 drops of phenolphthalein indicator into the aliquot.
    5.    Titrate against 0.1 N solution of NaOH till light pink coloured end point is obtained.
    6.    For coloured products, i.e. tomato products where judgment of light pink colour is difficult, titration may be done over a shaker, and digital pH meter may be used for continuously measuring pH of aliquot which would show a steady increase with more and more addition of 0.1 N NaOH. Titre value may be recorded when pH of 8.3 is obtained.
    7.    Record the titre value and calculate the acidity of the sample as per the given formula.

Introduction

Demonstration of biological nitrogen fixation is usually accomplished by estimating the total nitrogen through use of some modification of the Kjeldahl procedure. This technique is accurate and reliable whenever a medium initially low in nitrogen is employed.

Principle

The dried organism is digested with sulphuric acid. Organic and nitrate nitrogen is converted to ammonium sulphate and the ammonia gas is distilled into boric acid forming ammonium borate making weak boric acid alkaline. The ammonium borate is back titrated with standard sulphuric acid until the reaction mixture changes its colour from green to pink due to formation of ammonium sulphate. The standard acid used in back titration of ammonium borate is a measure of nitrogen content of the organism.

Principle: A weighed sample is dried in an oven at 60-70⁰C up to a period of time when weighing made at 2 hour intervals do not differ by more than 2-3 mg.

Materials Required

Fruit/ sample, refractometers, thermometers, standard solutions of known TSS, temperature correction Tables.

Procedure

    1.    Calibrate refractometers of all ranges to be used.
    2.    The TSS of the juices/pulps/fresh fruits can be measured with the one having lowest range i.e. 0-32º Brix while, for measuring the TSS of concentrates, syrups, squashes, jams, jellies etc. refractometers of the higher ranges are made use of.
    3.    Put a drop of material on to the glass surface of refrectrometer’s prism, cover gently with the lid and observe the TSS against light.
    4.    Measure the temperature of the liquid which is being evaluated and apply temperature corrections (Annexure III).
    5.    Record the corrected value as the TSS of the sample.