Printer Friendly

COMPARISON OF DRYING PROCESS AND PRESERVATIVES ON DRYING KINETICS, TEXTURE AND ANTIOXIDANTS RETENTION IN MULBERRY FRUITS.

Byline: M. K. Khattak, M. Hanif, M. Khan, M. Ramzan and Abdurab

Keywords: Drying Process, Preservatives, Mulberries, Texture, Antioxidants

INTRODUCTION

Horticultural plants, including mulberries have been an indispensable part of human life for ages. Ever since ancient times, their fruits, seeds, even roots and branches have been used to meet personal and social needs such as severing food, curing diseases and beautifying the planet (Erturk et al., 2010; Canan et al., 2016; Hricova et al., 2016; Yazici and Sahin, 2016). Mulberries belong to the Moraceae family, are small, cylindrical, juicy, safe to eat fruit that consists of a bunch of drupes. They are a rich resource of carbohydrates, proteins, potassium, minerals, vitamins, phenolics, flavonoids, anthocyanins and important antioxidants (Ercisli and Orhan, 2007; Ercisli et al., 2010). They have a good aroma and sweet agreeable taste, and are consumed as fresh or dried form. However, they have a very short shelf life and degraded quickly due to their high moisture content (Masood et al. 2008).

To preserve these mulberries, they are dried in open air and consumed in the extreme winter season in particular Asian countries, including Pakistan, Turkey, Iran, Uzbekistan etc. This method is very old and unhygienic, uncontrolled and not safe from the attack of microbes and pests. Almost 40% of the fruit is lost due to contamination and pest attack (Ali et al. 2016). The food industries of the world are at present looking for new advanced, alternative of open sun drying, inexpensive, hygienic and controlled preservation technology that yielding in good quality of dried fruits having minimum alteration in the quality attributes of dried fruits (Katsube et al. 2009). Additionally, the development of alternative technologies for dehydration and processing of fruits is necessary to reduce losses and obtain best quality value added fruits. Thus development of new drying technologies which are energy efficient and providing a base for quality drying is the goal of modern researchers (Hanif et al. 2016).

To develop new dehydrators and overcome the conventional open sun drying of fruits, numerous researchers have analyzed the dehydration of mulberries and other fruits. Luchai et al. (2013) studied the drying kinetics and quality attributes of mulberry (Morus alba. L) dried by a solar air heater and open sun, pretreated with different preservatives. They reported that hot air drying using solar air heater is quick and the quality of mulberries was very good as compared to sun drying. Akbulut and Durmus (2009) conducted experiments on white mulberry (Morus alba. L). They dried mulberries in the sun and a hot air provided by a 2.04 m2 solar air heater. They reported good kinetics and quality for samples dried by a solar collector. Katsube et al. (2009) studied the impact of drying process on quality attributes of mulberry (Morus alba. L). They reported that there is a significant difference found in between sun dried, solar dried and oven dried samples.

Solar dried and oven drying give much better results of antioxidants as compared to sun drying. Tasar et al. (2007) studied hot air drying of mulberries at temperatures lower than 50AdegC is the best practice to maintain phenolics, flavonoids and antioxidants. There are little data on different drying methods applied to different mulberry species under different preservatives and their effect on the drying kinetics and quality parameters such as texture and antioxidants retention. Thus the aim of the study was to find and compare different drying methods (Open sun, hot air by solar collector, and microwave), preservatives (control, Potassium meta bisulphate and Sodium benzoate) and species (Morus alba. L, Morus nigra. L and Morus laevigata) in the mulberries. The effects of the process variables over the proficiency of drying kinetics, texture and antioxidants retention of mulberries were determined.

MATERIALS AND METHODS

Mulberries: Three main species of mulberries grown in Peshawar, Pakistan namely White Mulberry (Morus alba. L), Black Mulberry (Morus nigra L.) and Himalayan Mulberry (Morus laevigata) were selected from the mulberry orchards of the newly developmental agricultural farm of the University of Agriculture Peshawar and stored at 1AdegC. Prior to drying each fruit is selected on the basis of size and more than 90% maturity. Mulberries were washed for 30 seconds with water at room temperature and dried with the help of tissue paper. The early characteristics of the mulberries were as given in Table 1.

Experimental Procedure: Before drying all the varieties were pretreated separately with 2% solution of Potassium Meta bisulphate (PMBS) and 1% solution of Sodium benzoate (SB) were used for achieving high quality and less degradation. One of the treatments was also considered as control without any pretreatment. After pretreatment with preservative, mulberries were subjected to be dehydrated until the moisture content becomes less than 20%. The drying conditions were as shown in Table 2. In sun drying, mulberries were put on clean trays and covered with polyethylene sheet. In a hot air drying, mulberries were placed in a dryer connected with a solar air heater that provided hot air for drying. The solar collector assembly is as shown in figure 1. In microwave drying, samples were subjected in a microwave oven (Model, JT-359 Whirlpool Ch). Weight lost data was recorded after each hour with the help of electronic balance. All measurements were performed three times.

Moisture Content (wet basis): Moisture content at each hour of drying was determined according to the procedure described by The Association of Official Analytical Chemists (AOAC) using equation 1.

Mc = mw/mt * 100

Where Mc is moisture content (% wb), mt is the total mass (g) while mw is water mass (g).

All the samples were dried for 8 hr per day.

Drying rate: Before drying rate, moisture ration was determined using equation 2 given by Hanif et al., (2016).

MR= a*exp (-k*t)

Where MR is moisture ratio

t is drying time (hr)

a and k are constants to be fitted in the graph of DR and MR.

Drying rate was calculated as derivatives of MR over time using equation (3) given by Hanif et al., (2016).

DR= dMR/dt

Where DR id drying rate (kg water. kg.dry solid-1)

t is drying time (hr)

Texture Analysis: Two bite compression tests were performed using texture profile analyzer (Model, TPAXT2 Stable Micro-Sys.UK) having a 5 mm cylindrical probe with 1.5 mm thickness. Samples were subject to a constant compression speed of 0.45 mm.s-1 at room temperature. The parameters analyzed before and after drying were hardness (g) and stiffness (g.mm-1).

Antioxidants Analysis: Antioxidants before drying and retained in the samples after drying were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity assay of mulberries. Measurements were made with 1.5 ml of DPHH added to different aliquots of ethanol and reacted for 2 hours at 25AdegC. The absorbtance spectrum was measured at 500 nm with a spectrometer (Model, Hitachi -UK-1900, UK). The sample mass to inhibit 50% DPPH was determined. The determinations were expressed as the percentage of antioxidants retention and calculated using equation 4 given by Anabel et al. (2017).

AAR= 100 -(AAo - AAt/AAo * 100)

Where AAR is Antioxidants Retention (%)

AAo is the initial and AAt is the final antioxidant retention capacity (%).

Statistical Analysis: Analysis of variance (ANOVA) was determined using three factorial completely randomized designs. Drying methods, preservatives and varieties were considered as three different factors. Results were expressed as mean+ SD. Means were compared using LSD at [alpha]= 5%. The effect on quality parameters were considered at 5% significance level.

Table 1. Initial Characteristics of the Mulberries prior to Drying.

Species###Moisture content###Total soluble###Water activity###Antioxidant

###(%)###solids (%)###capacity (DPPH)

White Mulberry (Morus alba L.)###85.01###11.50 oBrix###0.98###118 mg.g-1

Black Mulberry (Morus nigra L.)###83.76###12.11 oBrix###0.97###171 mg.g-1

Himalayan Mulberry (Morus laevigata)###85.85###11.12 oBrix###0.98###134 mg.g-1

Table 2. Drying Conditions of Mulberries at Different Drying Process.

Drying Methods###Temperature###Humidity###Time taken by drying

Open Sun###30 + 10###45-78%###48 hr

Hot air (solar collector)###50+5###10-15%###23 hr

Microwave###50+1###>10%###16 hr

Table 3. Moisture lost per hour from different species of mulberries as affected by different drying methods and preservatives.

###Drying Methods

###Open###Hot###Microwave###Mean

###Sun###Air

Preservative###Morus alba L.

Control###1.81###3.74###5.41###3.65

PMBS###1.79###3.71###5.37###3.62

SB###1.80###3.73###5.39###3.64

###Morus nigra L.

Control###1.87###3.82###5.49###3.73

PMBS###1.89###3.80###5.41###3.70

SB###1.86###3.81###5.44###3.70

###Morus laevigata

Control###1.76###3.71###5.38###3.62

PMBS###1.78###3.69###5.33###3.60

SB###1.76###3.70###5.34###3.60

Mean###1.81c###3.75b###5.40a

Table 3. Moisture lost per hour from different varieties of mulberries as affected by different drying methods and preservatives.

###Drying Methods

###Open###Hot###Microwave###Mean

###Sun###Air

Preservative###Morus alba L.

Control###0.029###0.041###0.047###0.039

PMBS###0.026###0.040###0.046###0.037

SB###0.024###0.041###0.046###0.037

###Morus nigra L

Control###0.031###0.042###0.049###0.041

PMBS###0.032###0.041###0.048###0.040

SB###0.031###0.040###0.047###0.039

###Morus laevigata

Control###0.029###0.039###0.048###0.039

PMBS###0.025###0.041###0.045###0.037

SB###0.026###0.040###0.039###0.035

Mean###0.028c###0.041b###0.046a

RESULTS AND DISCUSSIONS

Moisture loss and drying rate: Percent moisture lost per hour from the mulberries is given in table 3. The analysis of variance showed that drying method significantly (p < 0.05) affected the moisture loss per hour while the preservatives and varieties had a nonsignificant effect on mulberries. Maximum moisture of 5.40% was lost from samples dried by microwave followed by hot air drying with 3.75%, while a minimum moisture lost of 1.81% was recorded for open sun drying method. In species, black mulberries (Morus nigra L.) shown more moisture lost per hour as compared to the other two species. The reason for high moisture lost at microwave drying is a uniform drying environment and minimum relative humidity due to which the air had more capacity to extract moisture from the mulberries. On the other hand hot air provided by solar collector had temperature and humidity fluctuations causing relatively slow moisture lost.

Samples dried in the open sun showed a minimum moisture loss due to uncontrolled drying environment. The air was humid causing it to take less moisture uptake from the mulberries. The results are in accordance with the findings of Akbulut and Durmus (2009) and Akpinar (2008) who reported their results that hot air drying is 45% quicker than sun drying. Katsube et al. (2009) and Duygu (2011) also reported a decrease in drying time of 73% by mulberries dried by oven as compared to sun drying. The results that black mulberries (Morus nigra L.) lost more moisture were also reported by Taser et al. (2007). The drying rate of the mulberries is given in table 4. The analysis of variance showed that drying method significantly (p < 0.05) affected the drying rate of mulberries while the preservatives and varieties showed a nonsignificant effect.

A maximum drying rate of 0.046 kgwater.kg.dry solid-1 was recorded for samples dried by microwave followed by hot air drying with 0.041 kgwater.kg.dry solid-1 while the minimum drying rate of 0.028 kgwater.kg.dry solid-1 was recorded for open sun drying method. In Varieties, black mulberries (Morus nigra L.) showed more 0.047 kgwater.kg.dry solid-1 drying per kg of dry matter because of high moisture lost per hour. The results of drying rate are related with moisture lost per hour. These results are in accordance with the findings of Abdullah (2009) and Hanif et al. (2016) who reported their results that hot air drying is gives higher drying rates then open sun drying. These results are also in accordance with the findings of Doymaz (2004).

Texture: Statistical analysis of the data showed that the values of hardness (g) and stiffness (g.mm-1) were only affected by drying methods while there was no significant effects of preservatives and the species on the overall texture of the dried mulberries. The means of hardness (g) of the dried mulberries as compared with fresh are as shown in figure. 1. While that of stiffness is shown in figure 2. The results showed that the mulberries become harder and stiffness increases if we dry them in microwave oven. Less hard mulberries were obtained during sun drying while leathery and gently hard dried mulberries were obtained from hot air drying. The reason is slow and controlled drying by the help of hot air having minimum enthalpy and optimum capacity of gaining moisture from the samples. The results are in accordance with the finds of Enabel et al. (2016) who reported more hardness is samples dried by oven as compared to fresh.

Antioxidants Retention: Statistical analysis of the data showed that the values Antioxidants retention (%) was only affected by drying methods while there was no significant effects of preservatives and species on antioxidants retained in dried mulberries. The means of data as compared with fresh are as shown in figure. 3. More antioxidants of 52% retained in mulberries dried by hot air drying using solar air heater followed by 47% in microwave drying while a minimum of 41% antioxidants was recorded in samples dried in an open sun drying. The fact that minimum antioxidants retained in open sun drying is the ultraviolet rays in the sunlight. These ultraviolet rays degraded the antioxidants and reduce their amount in dried mulberries. The results are in accordance with the findings of Doymaz (2004) who reported the reduction in percent of antioxidants in open sun dried mulberries as compared to fresh. Taser et al. (2007) also reported reduction in antioxidants percentage as compared with hot air drying.

Conclusion: In food processing, drying process play a vital role in determining the final quality of dried products, particularly in terms of texture and antioxidants retention. Therefore, it is essential to select an optimal dehydration process. In this study, different drying process showed a significant Effect on drying kinetics, texture and antioxidants retention. Preservatives showed a significant effect on drying kinetics while it showed a nonsignificant effect on the texture and antioxidants. Although, microwave drying is fast, but it does not help to maintain a good texture and more antioxidants. From the study it was concluded that hot air drying using a solar collector is the best drying process to get valuable dried mulberries with good texture and more antioxidants.

Acknowledgments: The study was supported by Higher Education Commission (HEC) Pakistan under The National Research Program for Universities (NRPU) in the Project Title" Evaluation and Comparison of Flat Plate and Parabolic Trough Solar Collectors for Water Distillation, Water Heating and Drying of Fruits and Vegetables. Project No. 20-5176/NRPU/RandD/HEC-2014/135.

REFERENCES

Abdullah, A. (2009). Thin layer solar drying and mathematical modeling of mulberry. Int. J Energy Res. 33: 687-695.

Akbulut, A., and A. Durmus. (2009). Thin layer solar drying and mathematical modelling of mulberry. Int. J. Energy Res. 33:687 - 695.

Akpinar, E.K. (2008). Mathematical modelling and experimental investigation on sun and solar drying of white mulberry. J. Mech. Sci. Tech. 22: 1544-1553.

Ali, M., Y. Durrani, and M. Ayub. (2016). Effect of drying techniques and storage on mulberry (Morus alba) quality. Sarhad J. Agric. 32(2): 80-88.

Anabel, R., M.M. Rodriguez, M.L. Lemoine, and H. Mascheroni. (2017). Study and comparison of different drying processes for dehydration of rasbarries. J. Drying Tech. 35(6): 689-698.

Canan, I., M. Gundogdu, U. Seday, C.A. Oluk, Z. Karasahin, E.C. Eroglu, E. Yazici, and M. Unlu. (2016). Determination of antioxidant, total phenolic, total carotenoid, lycopene, ascorbic acid, and sugar contents of Citrus species and mandarin hybrids. Turk. J. Agric. For. 40: 894-899.

Doymaz, I. (2004). Pretreatment effect on sun drying of mulberry fruit (Morus alba L.). J. Food Eng. 65: 205-209.

Duygu, E. (2011). Drying and moisture diffusivity of white mulberry: Experimental and mathematical modeling. J. Mech. Sci. Tech. 25: 2711-2718.

Ercisli, S., and E. Orhan. (2007). Chemical composition of white (Morus alba), red (Morus rubra) and black (Morus nigra) mulberry fruits. J. Food Chem. 103:1380-1384.

Ercisli, S., M. Tosun, B. Duralija, S. Voca, M. Sengul, and M. Turan. (2010). Phytochemical content of some black (Morus nigra L.) and purple (Morus rubra L.) mulberry genotypes. J. Food Tech. Biotech. 48: 102-106.

Erturk, Y., S. Ercisli, A. Haznedar, and R. Cakmakci. (2010). Effects of plant growth promoting rhizobacteria (PGPR) on rooting and root growth of kiwifruit (Actinidia deliciosa) stem cuttings. J. Bio. Res. 43: 91-98.

Hanif, M., M.K. Khattak, M. Amin, M. Ramzan, S. Zakir, S. Ullah, and Z. Khan. (2016). Developing a flat plate solar collector for drying and water heating purposes. J. Sains Malaysiana. 45(3): 489-497.

Hricova, A., J. Fejer, G. Libiakova, M. Szabova, J. Gazo, and A. Gajdosova. (2016). Characterization of phenotypic and nutritional properties of valuable Amaranthus cruentus L. mutants. Turk. J. Agric. For. 40: 761-771.

Katsube, T., Y. Tsurunga, M. Sugiyama, T. Furuno, and Y. Yamazaki. (2009). Effects of air drying temperature on antioxidant capacity and stability of polyphenolic compounds in mulberry (Morus alba L.) leaves. J. Food Chem. 113:964-969.

Luchai B., W. Samappito, and S. Samappito. (2013). Phenolic composition and antioxidant activity of white mulberry (Morus alba L.) fruits. Int. J. Food Sci. Tech. 48, 934-940.

Masood, S.B., A. Nazir, M.T. Sultan, and K. Schroen. (2008). Morus alba L. Nature's functional tonic. J. Trends in Food Sci. Tech. 19:505-512.

Taser, O.F., S. Tarhan, and G. Ergunes. (2007). Effects of chemical pretreatments on air-drying process of black mulberry (Morus nigra). J. Sci. Ind. Res. 66: 477-482.

Yazici, K., and A. Sahin. (2016). Characterization of pomegranate (Punica granatum L.) hybrids and their potential use in further breeding. Turk. J. Agric. For. 40: 813-824.
COPYRIGHT 2019 Knowledge Bylanes
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2019 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Publication:Journal of Animal and Plant Sciences
Date:Jun 22, 2019
Words:3258
Previous Article:ESTABLISHMENT OF PROFICIENT IN VITRO MASS MULTIPLICATION AND REGENERATION SYSTEM FOR ENHANCED PRODUCTION OF STEVIOSIDE AND REBAUDIOSIDE A IN STEVIA...
Next Article:GENETIC DIVERSITY IN DRAGON FRUIT (HYLOCEREUS SP) GERMPLASMS REVEALED BY RAPD MARKER.
Topics:

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters