Studies on evaluation of physical properties of turmeric (Curcuma longa L.) rhizomes (Var. Kesar)]

Introduction

Mother earth has been nourishing all living beings since their evolution. Man has been using various natural plant products for various purposes since the time immemorial. A large number of products are produced as secondary metabolites by plants as a natural defence mechanism against disease and infection. Many of these natural products have pharmacological or biological activity that can be exploited in the area of pharmaceutical drug discovery as well as drug design. Natural medicines derived from plants have played a pivotal role in the health care of many cultures, both ancient and modern. Our ancient Indian system of holistic medicine widely known as "Ayurveda" uses mainly plant-based medicines or formulations to treat various ailments. Turmeric (Curcuma longa L.) is one of the holy plants that have a very ancient and long history of medicinal use, dating back nearly 4000 years. In Southeast Asia, turmeric is used not only as a principal spice but also as a component in religious ceremonies. Because of its brilliant yellow colour, turmeric is also known as "Indian saffron." Turmeric (Curcuma longa L.) is one of the world's most important spices. It is used to flavour and to colour foodstuffs. It is a principal ingredient in curry powder. Turmeric oleoresin is used in brine pickles and to some extent in mayonnaise and relish formulations, non-alcoholic beverages, gelatins, butter and cheese etc. The colour curcumin extracted from turmeric is used as a colourant. It is also used as a dye in textile industry. It is mainly cultivated in Asian countries including India, Bangladesh, China, Thailand, Cambodia, Malaysia, Philippines, and Indonesia (Ravindran et al., 2007) [1] . India leads global production and export, with a cultivated area of 291,000 hectares and estimated output of 1.116 million tonnes in 2024-25. Maharashtra, Tamil Nadu, Telangana, Karnataka, Madhya Pradesh, Odisha, and West Bengal are the top turmeric-producing states. In the first half of 2024-25 alone, India exported 137,000 tonnes of turmeric (https://en.wikipedia.org).

The turmeric plant is an herbaceous perennial, 60-90 cm high, with a short stem and tufted leaf. There are 7 to 12 leaves, the leaf sheaths forms the pseudo stem. The lamina is green above, pale green below, and has a length of 30-40 cm and width 8-12 cm. Inflorescence is a central spike of 10-15 cm length. 1-4 flowers are born in axil of the bract opening one at a time. Turmeric is harvested when the plants are between 7 and 10 months of age, when the stems and leaves start to dry out and die back. The whole plant is removed from the ground, taking care not to cut or bruise the rhizomes. The side (lateral) branches (which are known as the fingers) of the rhizomes are removed from the main central bulb (known as the mother). The mothers and fingers are heaped separately, covered in leaves and left to sweat for one day. The finger rhizomes are used for further processing while the mother rhizomes are stored for sowing purpose. The rhizomes have different forms such as spherical, slightly conical, hemispherical and cylindrical. They have brown peel covering just above an orange yellow flesh. As far as preservation, processing and storage are concerned, the information about the physical properties of an agricultural produce are very quiet important and necessary. These technical information are very crucial in design and development of different processing equipment such as cleaner, sorter, grader, dryer, grinder, conveyor and packaging machines for any specific crop. Besides, also very useful in their further processing. Nevertheless, there is limited published work on physical properties of turmeric rhizomes. Therefore, the present investigation was carried out to study the physical properties of turmeric rhizomes (Curcuma longa L.) (Var. Kesar). The study was conducted at the Department of Post-Harvest Technology, College of Horticulture, SDAU, Jagudan. The turmeric rhizomes (var. Kesar) were procured from the farm of the College of Horticulture, SDAU, Jagudan.

Materials and Methods

Procurement of raw material and sample preparation Turmeric rhizomes (var. Kesar) were procured from the farm at the College of Horticulture, S.D. Agricultural University, Jagudan, District Mehsana. After harvesting, turmeric rhizomes were collected and segregated into two categories: mother rhizomes and finger rhizomes (Plate 1). The mother rhizomes (Plate 2) were reserved for propagation purposes, while the finger rhizomes (Plate 3) were selected for the present experimental study. The fresh finger rhizomes were washed with water to remove adhering soil and extraneous materials (Plate 4). Any damaged or undesirable portions were manually discarded. Subsequently, the rhizomes were rewashed to ensure complete cleanliness prior to their use in the experiments.

Determination of physical properties of turmeric rhizomes

The physical properties of turmeric rhizomes, such as axial dimensions, arithmetic mean diameter (AMD), geometric mean diameter (GMD), square mean diameter (SMD), equivalent diameter, sphericity, aspect ratio, unit volume, surface area, and shape factor, were determined using standard methods (Mohsenin, 1986) [3] . Gravimetric properties including bulk density, true density, and porosity were also measured. In this study, measurements of these three axes were taken for 100 turmeric rhizome samples to calculate the average GMD. This metric provides an accurate representation of rhizome size by combining length, width, and thickness, which is essential for characterizing physical properties and designing processing equipment.

Arithmetic mean diameter (AMD)

The arithmetic mean diameter (AMD) was calculated using the following formula (Mohsenin, 1986) [3] :

Where, a = Major dimension, mm b = Medium dimension, mm c = Minor dimension, mm

This formula provides the average dimension used as a size parameter in physical characterization studies. This standard method is widely applied for calculating the arithmetic mean of irregular agricultural produce and is essential for engineering design and quality assessment.

Square mean diameter (SMD)

The square mean diameter (SMD) was calculated using the following formula (Mohsenin, 1986) [3] :

Where, a = Major dimension, mm b = Medium dimension, mm c = Minor dimension, mm

This formula computes the root mean square of the pairwise products of the dimensions, providing a representative mean diameter for the object, useful in characterizing the size for engineering and processing applications.

Equivalent diameter (EQD)

The equivalent diameter (ED) was calculated using the following formula (Mohsenin, 1986) [3] :

Where, AMD = Arithmetic mean diameter, mm GMD = Geometric mean diameter, mm SMD = Square mean diameter, mm

This formula calculates the average of the three mean diameters to represent an equivalent size parameter for the turmeric rhizome.

Sphericity (Ø)

The degree of sphericity (Φ) of turmeric rhizomes was calculated using the following equation described by Mohsenin (1986) [3] :

Where, a = Major dimension, mm b = Medium dimension, mm c = Minor dimension, mm

Here, the sphericity is defined as the ratio of the geometric mean diameter (cube root of the product of three dimensions) to the major dimension. This parameter expresses the shape of the rhizome relative to a perfect sphere and is an important property in fluid flow, heat, and mass transfer calculations related to the material.

Aspect ratio (AR)

The aspect ratio (AR) was calculated using the following formula given by Mohsenin (1986) [3] :

Where, a = Major dimension, mm b = Medium dimension, mm c = Minor dimension, mm

The aspect ratio expresses the ratio of width to length as a percentage and is used to describe the elongation or shape characteristics of the rhizome. This parameter is important for designing handling, processing, and sorting equipment based on the shape profile of the agricultural produce.

Unit volume (V) and surface area (S)

The unit volume and surface area of the samples were calculated using the standard geometric relationships proposed by Jain and Bal (1997) [4] . The mathematical expressions employed are as follows:

Surface area (S) = These equations enable precise estimation of the surface area (S) and unit volume (V) of irregularly shaped biological materials, such as rhizomes or seeds, by approximating them to an ellipsoidal form.

Shape factor (λ)

The shape factor (λ), which characterizes the geometric configuration of a particle in relation to its surface area and volume, was determined following the method described by McCabe and Smith (1984) [5] . The shape factor was computed using the following relationship: The parameter λ provides a quantitative indication of the departure of the sample's geometry from a perfect sphere. A value of λ=1represents a spherical shape, whereas deviations from unity indicate elongation or flattening of the sample.

Thousand rhizomes mass

The mass of one hundred turmeric rhizomes was measured using a precision electronic balance (Labtroniks, India) having a resolution of 0.01 g. The recorded mass of 100 rhizomes was subsequently multiplied by a factor of 10 to estimate the corresponding weight of 1,000 rhizomes, in accordance with the standard procedure for bulk weight determination.

Bulk density (ρb)

The bulk density of turmeric rhizomes was determined as the ratio of the mass of the sample to the volume it occupied in a known container (Plate 7). For this purpose, rhizomes were carefully filled into a cylindrical container of 1,000 cm³ capacity without applying any compaction. The mass of the filled container was measured using an electronic balance, and the bulk density was computed using the following expression:

True density (ρt)

The true density of turmeric rhizomes was determined following the procedure outlined by Mohsenin (1986) [3] . Fresh turmeric rhizomes were initially weighed using a precision electronic balance. The weighed samples were then carefully immersed in a graduated measuring cylinder containing toluene (C₆H₅CH₃), ensuring that the samples did not come into contact with the cylinder's walls or bottom (Plate 8). Toluene was selected as the displacement medium due to its favourable physicochemical properties, including a low tendency to penetrate the sample, low surface tension (allowing smooth flow over the material surface), minimal solvent action on organic constituents such as fats, a relatively high boiling point, and a low specific gravity. The true volume of the rhizome samples was determined based on the mass of toluene displaced, and the true density was calculated using the following relationship:

This method provides an accurate estimation of the material's intrinsic density, excluding interstitial air spaces, and is essential for evaluating physical properties such as porosity and structural compactness. Porosity is an important physical property that reflects the internal structural arrangement and compactness of the material. It influences various post-harvest and processing characteristics such as drying rate, rehydration capacity, and mechanical strength of the rhizomes.

Results

Axial dimensions

The axial dimensions of 100 samples from each of the three grades of turmeric rhizomes were measured. In grade I (length: 25-45 mm), length, breadth, and thickness varied from 26.50 mm to 45.00 mm, 9.30 mm to 39.56 mm, and 8.13 mm to 23.14 mm respectively (Fig 1 1). Similar results were reported by Ramos et al.

(2021) [6] and Thul et al. (2022) [7] . [8] , Thul et al. (2022) [7] and Basha et al. (2024) [9] found similar results.

Arithmetic Mean Diameter (AMD)

The [10] and Basha et al. (2024) [9] in their studies on turmeric rhizomes.

Square Mean Diameter (SMD)

The results showed that the SMD of fresh turmeric rhizomes ranged from 24.81 to 59. [9] also found similar results in their experiment on turmeric rhizomes.

Equivalent Mean Diameter (EMD)

The EMD of fresh turmeric rhizomes ranged from 17. 99 (2024) [9] also found similar results in their experiment on turmeric rhizomes.

Sphericity

The [7] also reported similar findings in their experiments.

Bulk density (ρb)

The bulk density of fresh turmeric rhizomes was observed to range from 438 kg/m 3 to 481 kg/m [9] and Balasubramanian et al. (2012) [8] .

True density (ρt)

The true density of fresh turmeric rhizomes ranged from 1062 kg/m 3 to 1108 kg/m 3 , 1040 kg/m 3 to 1075 kg/m 3 and 1092 kg/m 3 to 1111 kg/m 3 in grade I, grade II and grade III respectively. The corresponding Mean values of true density of rhizomes were 1079 kg/m 3 , 1060 kg/m 3 and 1102 kg/m 3 for grade I, grade II and grade III respectively (Table 5). Comparable findings were reported by Balasubramanian et al. (2012) [8] , Shelake et al. (2018) and Basha et al. (2024) [9] .

Porosity (ε)

The porosity of fresh turmeric rhizomes was observed in the range of 55 to (2024) [9] , Balasubramanian et al. (2012) [8] and Parmar and Dabhi (2022).

Acknowledgement

AcknowledgmentsThis is a bonafide research work carried out by Alok Nath. No part of this research papers has been published earlier in any journal or magazine.

References

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