THE EFFECT OF OSMODEHYDRATION PARAMETERS ON THE QUALITY OF <i>litchi chinensis</i>

Transcription

1 THE EFFECT OF OSMODEHYDRATION PARAMETERS ON THE QUALITY OF <i>litchi chinensis</i> Zaved Ahmed Khan*, Priya and Supraja Prasad Medical Biotechnology Division, School of Biosciences and Technology VIT University, Vellore , Tamil Nadu (INDIA)<BR><BR> Received June 24, 2009 Accepted September 05, 2009 ABSTRACT Osmodehydration is a novel approach towards preservation and is done by immersing the fruit in an aqueous solution with a greater osmotic pressure. It involves two major processes, one being the outflow of water from the fruit and the other being inflow of solute into the fruit and in this work we have studied the effect of osmodehydration parameters on the quality of lychees. (<i>litchi chinensis</i>).<br><br> Lychees not only help in reduction of obesity( low saturated fat content) and prevention of heart attacks(low cholesterol levels) but are also known for their anti-oxidant properties They are nutritionally very beneficial but the major disadvantage is that they are very expensive and grow seasonally, geographical prevalent and thus their preservation becomes an important issue. Though canned lychees are available in the market, microbes like <i>clostridium botulinum</i> pose a serious threat of spoilage which has been confirmed in our laboratory. Hence we intend to use osmodehydration as an effective solution for their preservation. Although sun drying has been practiced as a conventional method, this may give rise to problems like release of certain free radical ions which are harmful (carcinogenic) for human consumption and reduction in anti-oxidant levels. <br><br> Our work focuses mainly on varying the major parameters like concentration of the osmotic agent (d-fructose) and the temperature at which the process was carried out. The first phase was the removal of water using sugar syrup as an osmotic agent. The second phase of the dehydration was air drying where the moisture content is further reduced. By varying these parameters and monitoring the positive (osmodehydrated) and negative (air dried) controls we can determine the best conditions suitable for longer shelf life and safe consumption of lychees.we also found that by exposing the lychees to UV radiation for 120 seconds extends the shelf life.we will be assessing the effect of osmoregulation on antioxidant activity and its improvement by changing above parameters. Key Words : Lychees, Osmoregualtion, Food preservation, Antioxidant activity. INTRODUCTION and research, like the idea of dehydration for In this modern era of growing science preservation purposes, but how far we have and technology there have been considerable reached in maintaining the quality taste and advancements in the field of food technology shelf life of such products is a big question. The answer is not far away but is available in * Author for correspondence a novel approach to preservation called 70

2 osmodehydration. There is an everincreasing consumer demand for products with a relatively long life-span, which preserve the characteristics of fresh products. In the case of fruit, to obtain a fresh-like product implies certain operations such as peeling, cutting and packaging in syrup or often, partial dehydration of the product. In this case, osmotic dehydration has been the most effective method of dehydration with some advantages over other methods of drying, but it also brings some problems. As a technique for obtaining minimally processed fruits, osmotic dehydration (OD) is adequate, and does posses advantages over other drying techniques, yet it seems that some hydrosoluble components may escape into the osmotic solution (OS) during the process 1. Osmotic dehydration consists of the immersion of a solid food in watery solutions with a high soluble solid concentration. This technique causes a two-way mass transfer in crosscurrent: water and also some natural soluble substance flow out of the fruit into the OS, and in the opposite direction, soluble solids may be transferred from the solution to the fruit.the flow of soluble micronutrients, such as acids, minerals and pectins, from the fruit to the osmotic solution (OS) used to dehydrate the fruit when recycling it in successive osmotic dehydration (OD) operations, without reconcentrating can be easily quantified 2. Due to the kinetic of the OD operation it may be used to obtain products of reduced but still relatively high moisture content, classified as intermediate moisture products, but microbiologically stable due to reduced water activity 3.During OD, the fruits are not submitted to high temperatures, thus minimizing changes in sensory attributes, such as colour, aroma flavour and texture 4. Nevertheless, a loss of acids, vitamins, polysaccharides and minerals, which flow from the fruit to the 71 osmotic solution, has been observed 1,5,6. Furthermore, as opposed to other traditional drying treatments, OD does not affect the food structure because water elimination does not involve phase changes 7,8,9. However, one important factor related to this technique is that the osmotic solution used in the fruit OD process, commonly a sugar solution, is normally not re-used and can be considered as industrial waste, which not only greatly increases the cost of the osmodehydrated products, but also, if the sucrose syrup is discarded, once used, may result in loss of valuable natural substances such as vitamins, minerals, etc. Therefore, the possibility of recycling osmotic solutions or using them it in order to formulate some foods is very important for making the process economically and environmentally friendly 10. Reusing OS in more OD cycles is conditioned by compositional solution changes, as a progressive OS dilution after each cycle could slow down the mass transfer rate. When using in food formulations, in which the nutritional components lost by osmodehydrated fruits should be present, not only compositional but also physical changes such as in viscosity, electrical conductivity, etc., which occur, during fruit OD, have to be taken into account. It has been experimentally shown the use of osmodehydrofrozen fruit cubes in yoghurt. The osmotic dehydration for preserving papaya, pineapples and apples and influence of the process variables on product quality has been studied 4,l1. The Influence of solute temperature and concentration on combined osmotic and air drying have been

3 studied 12.The formal analysis of structural collapse and colour changes in osmo- air dehydrated peaches has been clearly demonstrated 13.On similar lines there have been studies on the physical, chemical and structural effects of osmotic pre-treatments in fruit processing 12.The influence of various process variables like sugar composition on osmotic dehydration of papaya,apricots and strawberries have been reported 7,14,15. The cultivation of Litchis in various parts of India has been well studied 16. Lychees are known for their nutritional benefits. They not only help in reducing obesity and prevent heart attacks but they are also known for their anti-oxidant properties. Since they are expensive and seasonal, preservation becomes an important issue. Though canned lychees are available in the market, microbes like Clostridium botulinum pose a serious threat of spoilage. Hence, we intend to use osmodehydration as an effective solution for their preservation. In certain parts of India like Kashmir,Uttaranchal and Shimla industries utilise the technique of sun drying for the large scale production of dehydrated lychees. This generally gives rise to two kinds of problems. Firstly sun drying causes the fruit to release certain free radical ions which are harmful for human consumption as they can sometimes prove to be carcinogenic in nature. On the other hand, sun drying also reduces the anti-oxidant levels by a large extent. Objectives Our focus is to attain such a nutritionally beneficial lychee with a longer shelf life and better quality. Our aim is to come up with osmo-air-dehydrated product which is 72 comparable to the fresh fruit in terms of colour, flavour and texture yet having the above mentioned desirable qualities. Hypothesis The basic principle involved here is the combination of osmosis and dehydration. In lychees endosmosis occurs mostly through the semi-permeable membrane (lychee skin).osmosis can bring about remarkable results as fructose is one of the best osmotic agents and dehydration is done by air drying the samples. Further the DPHH substance helps in determining the anti-oxidant concentrations in the fruit before and after treatment which gives us an idea regarding the success of the product. MATERIAL AND METHODS Fresh lychees (Litchi chinensis) were purchased from the local market and stored at 4 deg C. Prior to the actual procedure,they were peeled and then sliced into four symmetrical pieces. The lychees were then dipped in fructose solution which was used as the osmo-dehydrating agent. The experiment was carried out by varying the major parameters like concentration of the osmotic agent and the temperature at which the process was carried out. By varying these parameters and monitoring the positive (osmodehydrated) and negative (sun dried) controls we determined the best conditions suitable for longer shelf life and safe consumption of lychees. This involved pre-treatment by exposure to UV rays followed by these two phases. The first phase was the removal of water using sugar syrup as an osmotic agent. The second phase of the dehydration was airdrying where the moisture content was further reduced. We used the ph method for detection of microbial spoilage.

4 Reagents used a) 1 M fructose solution b) 3 M fructose solution c) Distilled water Materials used a) Petriplates b) Conical flasks c) Glass jars d) ph papers e) Forceps f) Peeler g) Swiss knife h) Parafilm i) Bunsen burner Preventive Measures Sterilise all glassware by autoclaving prior to the experiment Sterilise fructose solution after preparation Fructose solution has to be freshly prepared just before usage Instruments Used a) Laminar air flow b) Autoclave c) Drier d) IncubatorRefrigerator Procedure Lychees were osmodehydrated for 6 hours varying both parameters like 73 temperature and concentration of osmotic agent. The basic principle involved here is the combination of osmosis and dehydration. Osmosis is the movement of solvent molecules from their region of higher concentration to their lower concentration through a semi-permeable membrane. Here, endosmosis occured, semi-permeable membrane being the skin of the lychees. Various Petri plates with lychees in the following specifications were prepared 1) 1 M fructose solution at 40 deg C 2) 1 M fructose solution at 4 deg C 3) 3 M fructose solution at 40 deg C 4) 3 M fructose solution at 4 deg C 5) U. V sterilised 6) Sun dried (Negative control) They were sun-dried the for 48 hours which further reduced the moisture content. RESULTS AND DISCUSSION The samples were continuously monitored and changes in all the petriplates wzere noted. Microbial spoilage detection was done using the ph method, (Table 1) Table 1 : ph of solution in varying concentration S. no. Varying Parameters 1 1M at 40 deg C 3 2 1M at 4 deg C 4 3 3M at 40 deg C 4 3M at 4 deg C 5 5 U.V. sterlised 6 ph 6 Sun dried 4

5 Journal of Environmental Research And Development Vol. 4 No. 1, July-September 2009 Fig. 1 : showing the osmosis of lychees in 1M fructose at 40 0C Fig. 2 : Showing the difference in osmosis of lychees between 1M fructose solution and under control. Fig. 3 Fig. 4 Fig. 3 and 4 : Showing lychees in different concentrations of fructose solution at varying temperatures 74

6 CONCLUSION After the two phases namely osmodehydration and sun-drying, the ph of all the samples were noted and the degree of acidity determined the extent of spoilage. It was found that 3M concentration was more suitable than 1 M and further U.V. treatment helped improvise the process. Osmotic dehydration has been proposed in combination with air dehydration to improve quality attributes of air dried fruit pieces. The influence of the osmotic step and of the syrup composition on the chemical physical properties, structure collapse and colour changes of osmo-air-dehydrated lychees were studied. Colour attributes and geometric features were evaluated by image analysis to estimate volume reduction related to absolute moisture content. Sugars added during the osmotic step help to slightly decrease shrinkage during the first phase of the subsequent air dehydration, furthermore the osmo-dehydrated lychees showed the lowest structure collapse, retaining a better superficial appearance. The incorporation of sugars improved the colour stability during air dehydration, with fructose showing the highest protective effect. Thus we hope to commercialise this osmo-dehydrated product which is rich in nutrients(especially anti- oxidants), known for its medical importance as well as of good quality, better shelf life and consumer satisfactory. ACKNOWLEDGEMENT We would like to thanks VIT University for providing the basic infrastructural support and funds for carrying out this project. 75 REFERENCES 1. Peiró-Mena R., Camacho M. M. and Martínez-Navarrete N., Compositional and physicochemical changes associated to successive osmodehydration cycles of pineapple (ananas comosus), J. Food Eng., 79 (3), 842-9, (2007). 2. Peiró R., Dias V.M.C., Camacho M.M. and Martínez - Navarrete N., Micronutrient flow to the osmotic solution during grapefruit osmotic dehydration, J. Food Eng.,74 (3), , (2006). 3. Masmoudi M., Besbes S., Blecker C., and Attia H., Preparation and characterization of osmodehydrated fruits from lemon and date by-products, Food Science and Technology International, 13 (6), , (2007). 4. El-Aouar A.A., Azoubel P.M., Barbosa Jr. J. L., and Murr F. E. X., Influence of the osmotic agent on the osmotic dehydration of papaya (carica papaya), Journal of Food Engineering, 75 (2), , (2006) 5. Warczok J., Ferrando M., López F., Pihlajamäki A., and Güell C., Reconcentration of spent solutions from osmotic dehydration using direct osmosis in two configurations, Journal of Food Engineering, 80 (1), , (2007) 6. Falade K. O. and Igbeka J. C.,Osmotic dehydration of tropical fruits and vegetables. Food Reviews International, 23(4), , (2007) 7. Ledbetter C., Peterson S. and Jenner J., Modification of sugar profiles in california adapted apricots (prunus armeniaca L.) through breeding with central asian germplasm, Euphytica, 148 (3), , (2006).

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