Elsevier

Journal of Food Engineering

Volume 84, Issue 3, February 2008, Pages 413-419
Journal of Food Engineering

Optimization of osmotic dehydration of yam bean (Pachyrhizus erosus) using an orthogonal experimental design

https://doi.org/10.1016/j.jfoodeng.2007.06.003Get rights and content

Abstract

An orthogonal experimental design L9 (34) in triplicate was used to optimize the osmotic drying process of jicama or Yam bean (Pachyrhizus erosus). The effect of sucrose content, temperature, time of submerging and thickness of the fruit, on the osmotic drying process of Yam bean were tested. Maximal water loss was obtained when 10 mm fruit slices were submerged in a sucrose concentration of 60° Brix maintained at 60 °C for 2 h, while maximum impregnation was obtained when 5-mm slices were submerged in a 50° Brix solution maintained at 60 °C for 6 h.

Introduction

Jicama or Yam bean (Pachyrhizus erosus) tuber is exported to the United States of America and might be an alternative source of income for poor farmers in the South of Mexico. Yam bean tuber contains most essential amino-acids, such as alanine (380–3500 mg kg−1), arginine (720–6635 mg kg−1), aspartic acid (3870–35670 mg kg−1), cystine (110–1015 mg kg−1) glutamic acid (820–2855 mg kg−1), glycine (310–2855 mg kg−1), histidine (370–3410 mg kg−1), isoleucine (310–2855 mg kg−1), leucine (410–4425 mg kg−1), lysine (510–4700 mg kg−1), methionine (130–1200 mg kg−1), phenylalanine (320–2950 mg kg−1), proline (430–4330 mg kg−1), serine (470–4330 mg kg−1), tyrosine and valine (Duke, 1992). It also contains vitamins, such as niacin, riboflavin and thiamine, minerals, such as magnesium (160–1475 mg kg−1) and sodium (60–555 mg kg−1), and beta carotene (Duke, 1992). Yam bean tuber has a high moisture content, up to 90%, which makes it necessary to dry it to extend its shelf life.

Osmo-convective drying has often been used to dry vegetables and fruits (e.g. Saputra, 2001, Waliszewski et al., 2002, Xue et al., 2002), but little has been reported on the optimization of the osmotic drying process of Yam bean. The response surface technique has been used to optimize osmotic drying of mango (Madamba & Lopez, 2002), papaya Zapata-Montoya, Carvajal, and Ospina (2002) and melon (Fermin & Corzo, 2005). However, this method requires a lot of experiments as mass transfer depends on several variables, which on an industrial scale becomes very expensive. Optimization of osmotic drying using an orthogonal experimental design would reduce the amount of experiments and costs.

Orthogonal arrays are fractioned factorial designs that allow to test multiple independent processes variables within a single experiment. Orthogonal experimental design has been used to optimize culture media (Escamilla et al., 2000, Fontani et al., 2003, Ming-Tsung et al., 1997), but it has not yet been applied to optimize osmotic drying. The objective of this work was to determine the effect of temperature, sucrose concentration, immersion time and thickness of the fruit slice on water loss (WL), solid gain (SG) and moisture content reduction (MCR) during osmotic drying of Yam bean and to optimize the osmotic drying process using an orthogonal experimental design.

Section snippets

Treatments and experimental design

Yam bean fruits of a similar size were obtained from a local supermarket. Untreated fruits were hand washed and peeled. A TORREY slicer was used to get slices (30 × 18 mm) of three thicknesses, i.e. 5, 10 and 15 mm. A total of 100 g of the three different sizes of slices were submerged in a sucrose solution keeping the fruit/solution ratio between 1 and 8 to avoid dilution of the osmotic solution. The osmotic solution was gently agitated with a magnetic stirrer on a heating plate. Samples were washed

Water loss, solid gain and moisture content during osmotic drying

Water loss varied between 534 and 711 mg g−1, the solids gain between 70 and 229 mg g−1 and MCR between 280 and 571 mg g−1 (Table 1). The largest water loss was found for treatment 6 and the lowest for treatment 3. The largest solids gain was found for treatment 2 and the lowest for treatment 1, while largest MCR in treatment 4 and the lowest in treatment 2.

A polynomial regression was used to test the effect of several factors (two at a time) and to obtain the response surface (Table 2, Fig. 1, Fig. 2

Conclusions

Sucrose content, temperature, immersion time and thickness of the sample explained 93% of the water loss, 90% of the solids gain and 89% of the moisture content reduction. These high percentages indicated that the parameters selected to carry out the osmotic drying process, and their values were correctly chosen. Sucrose content, temperature, thickness and time had a significant effect on water loss and moisture content reduction; and temperature, thickness and immersion time had a significant

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