Ohmic Heating Assisted Turmeric Curing ; Performance Evaluation

OHMIC HEATING  ASSISTED TURMERIC CURING  ; PERFORMANCE EVALUATION

Abstract

Modeling of the thermal behavior of multiphase(particulate) food products with various electrical conductivities under ohmic heating has been a challenge. Distortion of electric field due to heterogeneous food properties and electrical conductivity distribution should be taken into consideration for accurate prediction of the thermal performance of ohmic heaters. The objective of this study was to develop a ohmic heating unit and model ohmic heating pattern of particulate food with three different electric strengths (25, 30, 35 V/ cm) , different temperatures ( 90 & 95˚C), and six substantially different  levels of time (5 -30 min). Turmeric rhizomes,particulate material which are  cured by ohmic heating and its effect are studied by analyzing different parameters like texture, curcumin, flour gel hydration properties, solubility and WHC. The dependence of electrical conductivity on temperature, voltage gradient and concentration were measured. System performance coefficient (SPC) is calculated for the set design. The SPCs depended strongly on the voltage gradient applied. The predicted temperature values were in good agreement with the experimental data. . Moreover similar starch modification was observed in ohmic heated sample when compare to traditional and improve traditional.

Abbrevations:

Nomenclature:

Cp : Specific heat capacity(J/kg K). D1: Empirical voltage gradient constant (S/m(cm/V)N1). Eloss : Rate of energy loss (W). E : Amount of heat (J) . E1 : Empirical concentration constant (S/m (mass fraction×100)-N2) .h : Heat transfer coefficient (W/m2K) . I : Current (Ampere) . k : Thermal conductivity of the sample (W/mK) .Kc : Cell constant (1/m).L : Distance between the electrodes (m). m : Mass of the sample (kg) .Q        : Amount of heat (J) . R : Resistance of the sample (m) , t :Time (s) . T : Temperature (◦C) . ů : Internal energy generation (W/m3) . v : Volume of the sample(m3) . V :        Voltage applied (V) . kV        :KiloVolt. Xw : Weight fraction of the water in the sample. ρ  :        Density of the sample (kg/m3). σ        : Specific electrical conductivity (S/m). B1 :        Empirical temperature constant (S/mK). B2 : Empirical temperature constant (S/mK). C2 : Empirical constant (S/m). acc. : Accumulated.  amb. : Ambient. exp. : Experimental.  SPC         : System Performance Coefficient. LPG : Liquid Petroleum Gas. SEM : Scanning Electronic Microscopy. RVA : Rapid Visco Analyzer. WHC : Water Holding Capacity. SP : Swelling Power. DSC        : Differential Scanning Calorimetry

XRD        X-Ray Diffraction . FTIR  : Fourier Transform Infrared Spectroscopy.

db : Dry basis. rpm         : Rotation Per Minute. MR : Moisture Ratio. SSE : Sum of Square of Error. df  : Degree of freedom. RMSE : Root Mean Square of Error ANOVA : Analysis Of Variance.  MC : Moisture Content.

Introduction :

Turmeric (Curcuma longa) is an erect perennial plant grown as an annual crop for its rhizome (underground root like stem bearing roots and shoots). It belongs to the same family as ginger (Zingiberaceae) and grows in the same hot and humid tropical climate. The rhizome is a deep bright yellow color and similar form to the ginger but slightly smaller. The plant originated in the Indian sub-continent and today India is the world’s leading producer and consumer of turmeric. It is also produced in China, Taiwan, Bangladesh, Indonesia, Sri Lanka, Australia, Africa, Peru and the West Indies. Turmeric plays an important role in Indian culture. It is an essential ingredient of curry, used in religious festivals, as a cosmetic, a cloth dye and in many traditional health remedies. The spice is sometimes referred to as ‘Indian saffron’.

Processing of turmeric rhizomes involves post- harvest treatments which include: curing, drying, polishing, and milling. Curing of the rhizomes is begun 3–4 days after harvest. The rhizome fingers and bulbs or mother rhizomes are separated and cured separately, and not whole, as the latter will take more time to cook (Sasikumar, 2003).

Recently, some quick heating technologies are applied in food viz. microwave heating, ohmic heating etc. which may be employed to overcome the short falls of traditional curing method to bring about desirable changes in texture, color and flavor. Ohmic heating is considered to be a novel thermal processing technique due to its mode of heat transfer in food for which it utilizes the electrical resistance of food material to the flow of current to generate rapid and uniform heat with in the food material volumetrically (Rawson et al., 2001).

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Ohmic heating has got many advantages over conventional methods of thermal processing such as Rapid and uniform heating, less damage to rheological, textural, organoleptic and nutritional properties, it is suitable for foods with particulate materials, energy efficiency etc. ( Kamali and Farahnaky,2015). Many researchers have studied ohmic heating and its effects on different aspects of various food materials especially in juice from fruits and vegetables. However, there is lack of literature related to treatment of particulate material by ohmic heating. In this study ohmic heating bath will be fabricated for particulate material (turmeric rhizome) and later effect of pre-treatment on texture and curcumin content will be determined. Moreover there is no scientific information available related to textural degradation of cured turmeric and therefore the mechanism of structural degradation and color fixation during curing of turmeric will be studied. Taking the above problems into consideration, the objectives has been proposed.

The aim of this study is; to develop laboratory scale ohmic heating bath for handling of particulate material and its performance evaluation. To study the effect of ohmic heating pretreatment on curing of turmeric rhizomes. To evaluate the Starch modifications during curing of turmeric rhizomes.

Materials and methods :

 Experimental set –up

The heating chamber of the assembly is fabricated as discussed by Darvishi et al., (2013) and Olivera et al., (2014) with some modifications. The compact heating chamber includes a cylinder made-up of Teflon containing two electrodes made of stainless steel at the axial ends of the cylinder. The capacity of the heating chamber is around 600±5 ml. Dismantling arrangements of the heating chamber are made for the cleaning purpose of cylindrical chamber or electrodes.