eBook Chapters

Theory

Bulk density of the food material play an important role in many applications such as drying, storing, separation of undesirable material, determining the purity of seeds, grinding, maturity evaluations, design of storage structures, etc. It is an important parameter in packaging requirement and is often 2-20% of true density. Bulk density is the density of material when stacked or packed in bulk. Bulk density of powder can be determined under loose conditions. Loose packing is defined as the state obtained by pouring a powder sample into a vessel without any consolidation.

Bulk density

Bulk density of the food material can be defined as the ratio of weight of an untapped material to its volume including the contribution of the inter-particulate void volume. There are two kinds of voids, voids between particles and void within particles. Weight of the material can be determined by weighing balance. Volume can be determined by measured dimensions or using liquid or gas or solid displacement methods.

Pore space or porosity : Porosity is an index of the relative pore volume in the soil or volume fraction of pores. Its value generally lies in the range of 0.3-0.36 (30-60%). Coarse textured soils tend to be less porus than fine textured soil, though the mean size of individual pores is greater in the former than in the latter. The total porosity, in any case, reveals nothing about the pore size distribution which itself is an important property.

Bulk density is the mass per unit volume of soil including pore space. The normal range of bulk density in most soils is ranging from 1.02 to 1.80 g / cm³. The bulk density of coarse textured soils will be on the higher side while organic soils will have lower bulk density.

Particle density is the mass of soil per unit volume excluding pore space. Pore space is that fraction of soil volume not occupied by solid particles.

Principle

The bulk density and percent pore space are determined from the apparent and true volumes of the soil measures by adding a known quantity of water to a measuring cylinder contain a weighed quantity of soil.

Aim : To determine the Calcium in plant sample.

Principle

Carbonate (CO₃) and bicarbonate(HCO₃) ions are species of the same acid, carbonic acid. Their proportionate content is a function of pH. The CO₃ starts to form as pH rises above 8.4. Carbonate and bicarbonate are generally determined in soil saturation extract by titration with 0.01 N H₂SO₄ to pH 8.3 and 4.5, respectively.

Apparatus Required

Burette, pipette, conical flask and mechanical shaker etc

Introduction

Carotenoids are pigments found in plants that contribute to photosynthesis and provide various health benefits. Measuring carotenoid content in leaves can help assess plant health, productivity, and the effects of environmental conditions. The determination of carotenoids typically involves extraction followed by spectrophotometric analysis.

Materials and Equipments

• Fresh leaf samples

• Acetone, hexane, or a mixture of acetone and hexane (for extraction)

• Mortar and pestle or homogenizer

• Centrifuge and centrifuge tubes

• Spectrophotometer • Volumetric flasks and pipettes • Analytical balance

Seafood has grown in consumption as it has become an important part of a diet. Simultaneously their safety is a rising concern for human health. However, seafood may contain harmful chemicals as well as biological agents that could pose health risks to consumers. Fishes are harvested from waters that are contaminated by varying amounts of industrial chemicals, heavy metals, pesticides and antibiotics. These contaminants may accumulate in fish at levels that can cause human health problems (e.g. carcinogenic and mutagenic effects).The seafood may also get contaminated with various pathogenic bacteria due to unhygienic handling practices, cross contamination of raw foods with cooked or ready-to eat foods, and lack of proper temperature control. Pathogenic bacteria can cause illness in human, either by infection or intoxication. Food borne infections are caused by swallowing live pathogens that grow within the body, usually in the intestinal tract. Intoxication is a condition caused by swallowing preformed toxins i.e. toxins produced by microorganisms in the food before it is eaten. Food can become contaminated at any point during production, distribution and preparation. Everyone along the production chain, from producer to consumer, has a role to ensure the safety of seafood.

Chlorophyll content serves as a vital indicator of plant health and photosynthetic efficiency, with higher levels reflecting robust photosynthesis and overall plant vigor, while lower levels may signal nutrient deficiencies, diseases, or environmental stresses. Assessing chlorophyll content helps evaluate plant productivity, as chlorophyll is essential for absorbing light and converting solar energy into chemical energy. Additionally, the chlorophyll-a to chlorophyll-b ratio provides insights into how plants adapt to various light conditions, revealing their light absorption efficiency and ability to cope with environmental changes. Measuring chlorophyll on a fresh weight, dry weight, and leaf area basis allows researchers and agronomists to gauge the effectiveness of agricultural practices such as fertilization, irrigation, and crop management strategies. It also aids in monitoring the impact of stress factors like drought, salinity, pollution, or pest attacks, which is crucial for developing strategies to enhance crop resilience.

Reagents: 80% acetone: - 80 ml acetone + 20 ml water = 100 ml

Procedure for Chlorophyll Extraction from Leaves

1. Sample Collection: Collect fresh, healthy leaves from the plant to be analyzed. Ensure that the leaves are free from dust, pests, and diseases.

2. Preparation of Leaf Samples: Rinse the leaves thoroughly with distilled water to remove any surface contaminants. Pat them dry with a clean paper towel. Weigh an exact amount (usually around 0.1-0.5 grams) of fresh leaf tissue using an analytical balance. Record the fresh weight accurately.

Abstract

The geochemical signature and vulnerability of groundwater of the East Coastal aquifers of  India from Pondicherry to Nagapattinam were determined. The coastal aquifers are fragile and this situation becomes more intense in aquifer systems like that of the Pondicherry to Nagapattinam region. A total of 136 water samples were collected during pre and post monsoon of 2008 and 2009 respectively. Out of which 45 samples for each pre and post monsoon from shallow groundwater and 23 samples for each pre and post monsoon from deeper groundwater.. The samples collected were analysed for major, minor cations and anions. Selected samples were also analysed for stable isotopes (d¹⁸O and dD). The analysed samples were studied for; their utility for different purpose, the nature of the geochemical classification, their variations in ion ratios, extent of sea water intrusion and the percentage of mixing, The study reveals that chief mechanism controlling shallow groundwater is the salts precipitated in the pore spaces during the Pre monsoon were leached and dissolved during the subsequent monsoon apart from sea water intrusion. Southern part of the study area  is more vulnerable than the Northern part of the study area.

Materials Required

Spectrophotometer, ethyl alcohol, beakers, pestle and mortar etc. 

Procedure

    1.     Preparation of sample extracts
        a.    Liquids : Centrifuge the juice at 5000 rpm for 4-5 min., and collect the supernatant. For liquid samples prepare a 40 % solution in ethyl alcohol. To 30 ml of the sample add 45 ml of ethyl alcohol and mix thoroughly. Filter through Watman 
No. 1 paper.

        b.    Semi-solid samples: To 15 g of blended sample add 15 ml of distilled water and 45 ml of ethyl alcohol. Mix thoroughly and filter through Watman No. 1 paper.
        c.    Dried products: Extract known quantity of sample (4-6 g) with 100 ml of 60% ethyl alcohol for 12 hrs and filter through Watman No. 1 filter paper.
    2.     Measure the absorbance of the samples at 440 nm for non-enzymatic browning and 400 or 420 nm for measurement of colour.
    3.     Prepare 60% ethyl alcohol solution as blank. Add 30 ml of distilled water to 45 ml of absolute alcohol and use as blank.

Aim

To determine the contours by cross-section method using dumpy level.

Materials required

Dumpy level

Leveling staff

Measuring tape

Wooden pegs/chain pins

Field book

Aim

To determine the contours by grid method using dumpy level.

Materials required

Dumpy level

Leveling staff

Measuring tape

Wooden pegs/chain pins

Field book

Aim

To determine the contours by radial line method using dumpy level.

Materials required

Dumpy level
Leveling staff
Measuring tape
Wooden pegs/chain pins
Field book

Description

Bucket elevator is one of the equipments used in the material handling to convey the material vertically. The lab model bucket elevator (Fig.34.1) consists of number of buckets/cups arranged to an endless flat belt. The belt with cups run vertically and cups are placed at a particular interval in the belt. The belt is wrapped over two pulleys, one at the top is called head pulley which receives power from an electrical motor 0.5 hp through suitable power concentration and rotates at required rpm. The belts, cups and pulleys are mounted on a steel frame. The grain from the hopper is reaches to the bottom pulley. The bucket is filled with grains during upward movement and is discharged at the top due to the centrifugal force. An outlet is provided at the top to collect the discharge grain. The capacity depends on the bucket size and seed of operation. For proper discharge of the material, the weight of the material in each cup should be equal to the centrifugal force created due to rotation.

Description

Screw conveyor is one of the equipment used in material handling to convey the material horizontally. The screw conveyor consists of screw blade, screw shaft, coupling, tubular trough, cover, inlet and outlet gates, bearings and drive mechanism. A shaft with spiral screw revolves in the tubular trough. The screw shaft is supported by end and hanger bearings. The rotation of screw pushes the grain along the trough. The pitch of a stranded screw which is the distance from the center of one thread to the center of the next thread is equal to its diameter

Materials Required

Soxhlet apparatus, petroleum ether, water bath, sample, grinder, weighing balance, filter paper, threads.

Procedure

    1.    Take the given sample and weigh it (A)
    2.    Dry the samples in an oven till there is no more weight loss and weight it (B)
    3.    Grind the sample into powder.
    4.    Place a weighed quantity of sample in filter paper, wrap the paper and tie it tightly with a thread so that no powder comes out of the paper during extraction. 
    5.    Pour approximately 100 ml of anhydrous ether into the bottom flask. Turn the heaters on. Set the temperature at about 40ºC.  
    6.    The ether will evaporate and circulate through the sample and again will come back to the flask. 
    7.    Repeat the process for about 16 – 18 hrs for complete extraction. 
    8.    Remove the sample and evaporate most of the ether from the mixture of crude fat and ether obtained during extraction.
    9.    Evaporate excess of ether from the crude fat sample by evaporation on a water bath. Evaporate till it is free from the fumes of ether. Record the weight (C).

Materials Required

Sample, Liebig condenser, digestion flasks (700-750 ml cap), conical flasks, filtering cloth (thick linen cloth for clear filtration) reagents, muffle furnace, crucibles.

Reagents

    1.    0.255 N Sulphuric acid solution : Dilute 2.5 g (1.36 ml) of concentrated H₂SO₄ to 200 ml. Ensure correct concentration by titration.
    2.    0.313 N Sodium hydroxide solution: 2.504 g NaOH / 200 ml water nearly free from sodium carbonate. Ensure correct concentration by titration.
    3.    Asbestos Chips: gooch grade, medium fibre, acid wash and ignited
    4.    10% Potassium sulphate (K₂SO₄) solution: Dissolve 10 g of Potassium Sulphate (AR) in water and make up to 100 ml.

Breaking of soil aggregates and dispersion followed by a rapid drying leads to rearrangement and coherence of soil solids in the form of surface crust. The cohesion exhibited by soil upon drying is directly related to surface crusting and clod formation. The formation of soil crusts and hard clods is a major structural feature of soils. Seedling emergence of cereal crops is generally controlled by point resistance around the shoot tip (Richards, 1953). Penetrometer, which measures the resistance to vertical penetration in soil, is an effective instrument to evaluate the crust strength. A relationship between penetration resistance and seedling emergence would serve as a guide to ensure optimum soil condition for a desired plant density.

Apparatus and Accessories

Penetrometer, moisture box, trowel, electronic balance and oven.

(Method of Olbrich et al., 1971)

Jones and Ekman (1960) showed that ¹⁴⁴Ce is absorbed to a very small extent in the gut of the ruminant and suggested its use as a marker in digestibility trials. Huston and Ellis (1968) studied the affinity of radioactive cerium for feedstuffs and digesta particles in vitro experiments and found that cerium is rapidly absorbed onto and remained tenaciously bound to  digesta particles. Ellis and Huston (1968) tested radioactive cerium as a particulate flow marker in sheep with favourable results.

Experimental Procedure
Three Holstein bulls weighing 315, 239 and 305 kg and one Holstein steer weighing 327 kg are used. Twice daily, at 9.00 am and 9.00 pm, they are fed 3.4 kg of a balanced ration, meeting NRC requirements for normal growth and maintenance.

Aim

To study the determination of drying rate of agricultural products

Problem

In a drying experiment on paddy at an air temperature of 60ºC, the following data were obtained. Prepare a drying rate curve for the experiment. Initial weight of the sample is 1250 gm and initial moisture content is 35% (d.b).

Electrical conductivity of the soil is the quantity of electricity in coulombs that passes per second per cm3 of the soil solution under an applied potential difference of 1 volt. It is written as EC in abbreviated form and is expressed in millimohs cm-1 or dS m-1 (deciSiemen m-1). Current flows in the soil solution due to presence of soluble salts like Cl- , SO2- 4 and NO3 - of Na+, K+ Ca++ and Mg++. These salts fully dissociate in water to their constituent cations and anions and the current is carried by those cations anions in the soil solution.

1. Introduction

Organisms are known to experience stress when environmental conditions, such as temperature, photoperiod, and humidity deviate from their optimal range. Organisms that respire aerobically constantly generate reactive oxygen species (ROS) through metabolism and employ antioxidants to reduce excess ROS formation and maintain a redox balance (Juan et al., 2021). ROS play crucial roles in cell signaling (Sies and Jones, 2020), homeostasis, cell death, immune defense against pathogens, and the induction of mitogenic responses (Dröge, 2002). Therefore, optimal environmental conditions maintain a balance between ROS formation and antioxidant processes in all living organisms.

Procedure

• Take 1 g soil in a 50 ml beaker

• Add 25 ml 1M KCL solution 

Reagents

• Buffer solution : Dissolve 67.5 g of Ammo. Chloride in 200 ml distilled water. Add 570 ml Ammonium solution. The volume make up to 1 ltr.

• EBT : 0.2 g in 25 ml methanol.

Calcium (Ca) and magnesium (Mg) are the two most abundant alkaline earth cations in soils. They both occur as soluble ions in soil solution, exchangeable, non-exchangeable and in organic material. Soils from arid regions are richer in Ca (1-2% CaO), while those from humid zones have a low content (0.01-0.02% CaO). On the other hand exchangeable Mg is found in very small quantities in calcareous soils. Sometimes, in acid soils, Mg²⁺ represents the largest quantity of the sum of exchangeable bases.

Principle

The method is based on the principle that calcium, magnesium and a number of other cations form stable complexes with versenate (ethylendiaminetetraacetic acid disodium salt, EDTA) at different pH. A known volume of standard calcium solution is titrated with standard 0.01N EDTA solution using murexide (ammonium purpurate) indicator in the presence of NaOH solution.

The end point is a change of color from orange red to purple at pH 12 when the whole of Ca forms a complex with EDTA. Calcium plus Mg are also present in the solution and can be titrated with 0.01N EDTA using buffer solution and a few drops Eriochrome Black T indicator. The end point is a change of color from red to blue at pH 10. Beyond pH 10, magnesium is not bound strongly to Erichrome Black-T indicator to give a distinct end point.

Carbonate is a natural constituent of many soils occurring as sparingly soluble, alkaline earth carbonate, chiefly as calcite and dolomite. Most carbonate minerals found in local soils are calcite and account 90% of total soil carbonates. The determination of total carbonate such as CaCO₃in soil is of great interest on account of high useful ess for diagnosing soil status in terms of structure, texture, biological activity or nutrient content. In calcareous soils carbonates exert a major influence on the chemical properties. Also carbonate content is used as a differentiating criterion for some classes at the family level of soil taxonomy.

Principle

A qualitative rapid test for free calcium carbonate is made by adding 10 mL of diluted HCl(1:3) to about 5 g of air dry soil on a watch glass and observing the intensity of effervescence which results from the evolution of CO Based on the . degree of effervescence the amount of calcium carbonate present in the soil can be broadly categorized into “traces or negligible, low, medium, high and very high”. Soils having traces to low amounts of calcium carbonate do not pose any problem. But those showing medium to very high degree of effervescence, a separate quantitative analysis should be carried out using Puri’s rapid titration method.

54.1. Aim

To determine crude fibre in given samples.

54.2. Theory

Fibres can be classified into four categories like crude fibre (cellulose); acid detergent fibre (cellulose + lignin); neutral detergent fibre (cellulose + lignin + hemicelluloses) and total dietary fibre (Cellulose + lignin + hemicelluloses + pectic substances). Crude fibre is the organic residue of a sample. A fat free sample is treated with boiling sulphuric acid and subsequently with sodium hydroxide. The residue after subtraction of ash is regarded as crude fibre.

54.3. Reagents/ Apparatus/Glassware

1. 0.255 N Sulphuric acid solution

2. 0.313 N Sodium hydroxide solution

3. 10% Potassium sulphate solution

4. Ethanol

Limitation of Weende Method

The partition of carbohydrate into fiber (CF) and nitrogen free extract (NFE) is presumed to represent a separation of less digestible starch and sugars. However, in 20 to 30 percent feeds listed by Morrison, the NFE is less digestible than the CF. This comes about for several reasons, the most important of which is the CF method (successive boiling with dilute sulphuric acid and sodium hydroxide) does not recover all the fiber and large portions of fibrous constituents  are extracted into the NFE. The most  important of these fractions are lignin and hemicellulose are dissolved by both acid and alkali. The basic error of the NFE concept is the assumption that if constituents are soluble they are digestible. Lignin, the rigid component of wood, not only is indigestible but lowers the digestibility of substances with which it is associated.

Another portion of the indigestible part of NFE arises from an artifact in the calculation of faecal NFE, where it is presumed that faecal nitrogen is protein (N x 6.25). Actually, 80-90 percent faecal nitrogen is NPN and is composed of bacterial residue in which the ratio of organic matter to nitrogen is about 1:4. Thus, part of the faecal NFE arises by an underestimation of the organic matter associated with faecal nitrogen.

Fructose, a keto-hexose (called as fruit sugar), is usually accompanied by sucrose in fruits and estimated by the methods of Ashwell (1957).

Materials

Resourcinol reagent: Dissolve 1g resorcinol and 0.25 g thiourea in 10 ml glacial acetic acid. This is stable in the dark.

Dilute HCl: Mix five part of conc. HCl with one part of distilled water.

Standard fructose solution: Dissolve 50mg of fructose in 50 ml water. Dilute 5 ml of this stock soln. to 50 ml for a working standard.

[Schoonover (1952) Method]

Introduction

Sodic (Alkali) and Saline-Sodic soils are characterized by the presence of large amounts of sodium, as high as 15% or more, on their exchange complex. As a result of this, the pH of soils increases beyond 8.0, causing nutritional imbalances, elimination of soil organic matter, deterioration of soil physical condition, etc., besides affecting the soil biotic community. Gypsum (CaSO₄. 2H₂O) is commonly used for the management of such soils, when applied in right amounts and size.

Principle

A given weight of soil is equilibrated with a known amount of Ca solution, and the amount of Ca, left in the solution is determined by EDTA titration. The difference between the amount of Ca added and the Ca left in the solution, gives the amount of Ca exchanged. In practice, gypsum of about 1/3 of the value, obtained by this method, is satisfactory in most cases.

Hydraulic conductivity is an important soil property that determines the ability of a soil to transmit water. A method of measuring hydraulic conductivity of saturated soil using undisturbed soil core is described in this exercise.

Principle

Flow of water across a soil layer or a sample of known dimension can be best described by Darcy’s law expressed as:

Infiltration rate refers to the volume of water entering into the soil per unit area in the unit time, when the soil is subjected to a shallow depth of ponding at the surface. Under continued ponding, the high infiltration rate in the beginning decreases to a constant value, known as final infiltration rate. The reduction in infiltration rate is due to combined effects of reduced hydraulic gradients, dispersion of aggregates, blocking of pores, cracks and channels, and swelling of colloids. Numerous techniques for measurement of infiltration rate have been developed to meet specific needs but use of double-ring infiltrometer has given consistent result in a variety of conditions.

Principle

In double-ring infiltrometer method, a small representative area in the field is bounded by two concentric metal rings (Figure 17.1) which permit impounding of water over the soil within the rings. The rate fall of surface of water ponded on the soil in the inner ring is taken as the rate of water intake or infiltration rate. In the cropped field, infiltration rate can be measured only within the rows and for which the diameter of the cylinders may be changed to meet the specific needs. The measurements under wetland conditions should be made from a distance of about 40-50 cm to avoid pressure effects.

Principle

When water is ponded inside the concentric metallic rings driven into the soil, the rate of recession (fall) of the water level, or the rate of water withdrawn from a supply source used to maintain a constant head of water on the soil surface, gives the infiltration rate of the soil.

During infiltration of water into the soil, appreciable lateral movement of water may also occur. To avoid the error due to this lateral movement, two concentric rings are used. Equal heights of water are to be maintained in both the rings. The infiltration is measured in the inner ring only. The rate of water intake per unit area varies markedly with the size of the rings and the depth of the soil to which they are driven into. Infiltration rate studies are preceded by the profile, initial soil moisture and any other problems of the region in which the soil is located.

Introduction

The balance between soil organic matter (SOM) levels and nutrient cycling are the key to sustained productivity of agricultural system. Both are closely related through microbially driven mobilisation/immobilisation processes. Three major models have been recognised for C pool viz. Labile C, non-labile C and recalcitrant. The models have been characterised on the bases of their half-life period. The labile C includes oxidisable C (with KMnO4), microbial biomass C (soil carbohydrates) and soil fauna exudates (polysaccharides). Its half-life period is from a few hours to a few days. The non-labile C includes aggregate C and its turn over time is from a few months to a few years while the recalcitrant (stabilised C) includes humic fractions and charcoal C having the turn over time of hundred years. Thus fractionation of SOM is carried out on the bases of humic substances, dissolved organic C, natural C13 abundance, microbial biomass C and ease of oxidation of C. The latter method provides qualitative characterisation of soil C.

Leaf Relative Water Content (RWC) is a key indicator of plant water status and is used to assess water stress, physiological health, and the efficiency of water use in plants. It reflects the amount of water in the leaf relative to its maximum water capacity and is a useful measure in plant physiology and stress studies.

Materials and Equipment

• Fresh leaf samples

• Analytical balance

• Oven or drying equipment

• Desiccator

• Caliper or ruler

• Distilled water

• Petri dishes or similar containers

• Weighing boats or paper

The lime requirement (LR) of an acid soil is the amount of lime needed to neutralize the acidity from an initial condition to some target soil pH, like 7.0. Different methods are used to calculate a LR for specific soils. Lime requirement tests will always recommend adding enough lime to neutralize all the acidity associated with soil pH, much of the salt-replaceable acidity, and some of the residual acidity.

[Shoemaker, Mc Lean and Pratt (SMP) Method, 1961]

Introduction

For proper plant growth, the soil should have a pH between 6.5 and 7.5, though there are certain plants which can grow satisfactorily at low pH, for example, tea, and at high pH, for example, sugar beet. In India, acid soils are located mostly in Eastern, Southern and South Central parts though some soils, at higher elevations, in North India are acidic.

In order to achieve maximum yield and sustained productivity through efficient soil management practices, it is essential to lime an acid soil, as it has considerable influence on soil environment, besides correcting soil acidity.

Several methods have been proposed to determine the lime requirement of acidic soils, to raise the pH around 6.5. The soil pH value alone, however, is not a good criterion for lime recommendation, because of variations in the exchange acidity of soil, and the nature of crops which may not require as high as this pH to produce maximum yield. Of these various methods proposed, the Shoemaker / SMP method was found satisfactory.

The recent trend of liming is to use it as a fertilizer rather than as amendment so as not to disturb heavily the natural environment while ensuring sustained productivity.

Aim : To determine the Magnesium in plant sample.

(Keen-Rackzowski/Hilgard Apparatus Method)

Principle

With the capillary rise of water, the soil immediately above a water table gets saturated. The height upto which the soil is saturated depends on the texture, structure and packing of the soil mass. The experimental technique discussed herein permits approximation of maximum water holding capacity while determining the amount of water held in the soil at the point of saturation.

Mechanical damage is inflicted on seeds during harvesting, threshing drying, processing and handling. Injury may occur from any kind of physical abuse. Threshing abuse probably is most serious but, seed conditioning and handling also contribute to seed injury. High temperatures during drying or drying too quick or excessively can cause injury. Susceptibility to mechanical injury increases as the moisture content of the seed decreases. Effect of all individual impacts received by the seed appears to be cumulative in total seed damage. Cereals are largely immune to mechanical injury presumably because of the protective outer structures, the palea and lemma. Large sized legumes are more suscepitable. Small seeds tend to escape injury during harvest and seeds that are spherical tend to suffer less damage than elongated or irregularly shaped ones.

Introduction

Dye reduction tests show the comparative activity of the bacteria in milk, therefore are considered as rough indicator of the number of bacteria per millilitre of milk. These tests find wide application in dairy industry especially in grading of milk for manufacturing purposes. The small amount of equipment, materials and simplicity of method permit simultaneous testing of several samples. Since it combines speed and adaptability, this test may be used in milk plants, receiving stations, condensing plants, cheese factories and similar establishments to rapidly grade incoming milk.

Principle

It is based on the observation that the colour imparted to milk by a small amount of methylene blue disappears in a time, the length of which is dependant largely upon the number of microorganisms

Introduction

Resazurin has high tinctorial value (related to colour), imparting characteristic blue colour. Resazurin test gives us indirect information concerning bacterial content and /or activity. Resazurin is also sensitive to the reducing action of leucocytes. The results of this test are comparatively less affected by antibiotic residues in milk than methylene blue reduction test.

Principle

Reduction of dye is indicated by a gradual colour change through various shades of purple and mauve to full pink, at which point the resazurin completely changes to resorufin.

All atoms can absorb light at certain discrete wavelengths corresponding to the energy requirement of the particular atom. When at ground state the atom absorbs light it is transformed into the excited state. It is the same atom containing more energy. This energy is measured in relation to the ground state and a particular excited state say for example in case of Na may be 2.2 eV (electron volts) above the ground state.

Each transition between different electronic energy states is characterized by a different energy and by a different wavelength. These wavelengths are sharply defined and when a range of wavelengths is surveyed, each wavelength shows as a sharp energy maximum (a spectronic line). These characteristic lines distinguish atomic spectra. The lines, which originate in the ground state of atom, are most often of interest in atomic absorption spectroscopy. These are called the resonance lines. The atomic spectrum, characteristic of each element, then comprises a number of discrete lines, some of which are resonance lines. Most of the other lines arise from excited states rather than the ground state. The lines of excited states are not useful generally in atomic absorption analysis as most of the atoms in a practical atomizer are found in the ground state.

A. Estimation of Calcium

Requirements : Pottasium permanganate solution (0.1N) – Dissolve by heating 33g of potassium permanganate in 1000ml distilled water and allow to stand in coloured bottle for several days. Filter contents through 6mm thick film of asbestos mat on Gooch crucible.

Asbestos mat – Digest asbestos with dilute hydrochloric acid(1:3) for 2-3 days, wash free from acid and digest with 10% sodium hydroxide for few days, wash free from alkali. Digest with dilute Nitric acid(1:3) for several hours and wash. Shake with water into fine pulp and digest with 0.1N potassium permanganate solution that has been acidified with dilute sulphuric acid (1:3), for 1 hour and wash. Use this pulp for layering 6mm film on Gooch crucible.

Dilute hydrochloric acid (1:4), Ammonium hydroxide solution (1:1), Saturated ammonium oxalate solution, Diluted sulphuric acid (1:4)

Materials Required

Sample, hot air oven, weighing balance, crucibles, muffle furnace, lead pencil / marker etc.

Procedure

    1.    After following the procedure for the determination of moisture (in silica crucibles as given in previous chapter) the same sample can be used for the determination of ash. 
    2.    Heat the dried sample in the silica crucibles over a heater/hot plate/burner to burn the carbon.
    3.    When it becomes completely black and no more smoke comes out of the sample, shift them to muffle furnace.
    4.    After heating the samples in muffle furnace, all the marks of pen / pencil/ marker are lost, so one would not be able to identify the samples and error of weights may occur. Therefore, it is advised to place the samples in the furnace in one or two rows and draw the diagram on a piece of paper for identification purpose.

Materials Required

Fruit, vegetable or product sample, hot air oven, weighing balance, crucibles, petri plates, lead pencil / marker etc.

Procedure

    1.    Take crucibles  or petri plates and record the tare weight of crucibles / petri plates (C) and mark them
    2.    Cut the sample into small and thin pieces (if solid)
    3.    Put the sample into the crucibles / petri plates in three replications
    4.    Record the weight of crucibles + sample (C + S)
    5.    Put in hot air oven for drying at 70 + 2ºC.
    6.    Record the loss in weight after every 1-2 hrs till it becomes constant
    7.    Calculate the moisture and total solids. 

Theory

This type of moisture measurement is called brown-duvel fractional distillation method. The method is recognized as an official method for determination of moisture content. In this method, directly measures the volume of moisture in cubic centimeter. This apparatus consists of flask, burner, thermometer, condenser, graduated cylinder. This apparatus consists of flask in which grain sample is boiled with mineral oil.

Theory

Indirect methods are based on the measurement of electrical properties of the grain that depends upon moisture content. There are two indirect methods namely (i) electrical resistance and (ii) dielectric methods are used. The electrical conductivity or resistance of a product measures its moisture content at a given compaction and temperature. The electrical resistance is depends on its moisture content, degree of compaction, grain temperature and impurities present in the sample. The universal digital moisture meter measures the electrical resistance of the grain at a given compaction. Universal moisture meter gives fairly accurate readings of moisture content on wet basis. In dielectric method, grain moisture content can be measured with the help of dielectric properties of the grains.

Theory

The amount of moisture in a product is given on the basis of the weight of water present in the product and is usually expressed in percent. Moisture content is designated by (i) wet basis (wb) and (ii) Dry basis (db). The moisture content on dry basis is more simple to use in calculation as the quantity of moisture present at any time is directly proportional to the moisture content on dry basis.

Preparation of the material: Common minute material for analysis in Waring blender for 1 to 2 minutes. Do not over heat. Pass it through No.60 sieve and put is in airtight container.

Procedure: Take 2 to 3 g sample in duplicate in pre-dried and pre-weighed 7 cm diameter aluminium dishes. Remove the dish cover and put them in vacuum oven and dry for 6 hours at 88°C and 26-22 inch vacuum. During this process, admit to oven a slow current of air (2 bubbles per second) dried by passing H₂SO₄ replace the cover, cool it in desiccators and weigh again.