Title of Invention

PROCESS FOR THE RETENTION OF PUNGENCY DURING DEHYDRATION OF FEED

Abstract

The present invention relates to a process for the retention of pungency during dehydration of feed such as onion and garlic. The present invention particularly relates to a process for dehydration of onion rings and garlic cloves with infrared and hot air, intermittently, which enables the product to retain higher amount of pungency over hot air dehydration and thereby improves the product quality. The novelty of the present system is that infrared radiation is applied intermittently and hot air is blasted simultaneously through the material bed to enhance the rate of heat and mass transfer. The rapid heat and mass transfer during dehydration reduces the drying time, which in turn minimizes the loss of flavor. Intermittent radiation with hot air blast reduces the damage to the cell and thereby increases the retention of the flavor component.

Full Text

FIELD OF INVENTION The present invention relates to an improved process for the retention of pungency during dehydration of feed such as onion and garlic. The present invention particularly relates to a process for dehydration of onion rings and garlic cloves with infrared and hot air, intermittently, which enables the product to retain higher amount of pungency over hot air dehydration and thereby improves the product quality. BACKGROUND AND PRIOR ART Application of infrared heating is recently been adopted for use in certain food processing applications, because of its superiority in terms of costs and the product quality (color, organoleptic and nutritional value) as compared with conventional heating. Infrared radiation is part of an electromagnetic radiation having wavelength in the range of 0.78 |am-1000 urn. Infrared heating offers many advantages over conventional heating under similar processing temperatures and is being preferred over conventional heating in operations such as drying, blanching, baking and roasting. When the substance is exposed to infrared radiation, the radiation first impinges on the surface of the material and penetrates it. Depending on the properties of the treated material and the temperature of the radiator on which the length of the wave depends, the infrared rays may be capable of penetrating into the depth of the material. On the increase of the radiator temperature, the wavelength decreases and the penetration depth increases. The incident radiation causes the change in the vibrational state of the atoms and molecules. When the frequency of the incident radiation is close to the value of the frequency of the natural oscillation of the atoms, then the amplitude of the imparted vibrations of the atoms increases. At the same time the coefficient of the energy absorption is also increased. The change in the vibrational state of the atoms and molecules generates heat energy within the material. Color and flavor are the main quality attributes of dried onions. Browning discolorization, loss of pungency and poor rehydration are the major problems of dehydrated onions. The pungency of onion arises as a result of the interaction of S-substituted L- Cystine sulfuoxide derivatives and Alliinase enzyme when the integrity of the onion tissue is destroyed. The interaction results in the unstable Sulfonic acid (-RSOH) besides Ammonia and Pyruvic acid. The Sulfonic acid further reacts to give the sulfur containing odoriferous substances, which impart the characteristic pungency to onion. Since the quantum of Pyruvic acid produced is proportional to the flavor compound produced, it has been used as the index for representing the flavor strength of onion. During convective dehydration of onion, the heat transfer takes from the hot air to the material and further transfer of heat within the material takes place by conduction. This leads to a longer processing time, which results in higher loss of pungency. Application of infrared radiation for dehydration could be a good alternative, which overcomes the above drawbacks. Application of intermittent infrared radiation with hot air blast increases the mass and heat transfer rate, which reduces the processing time and improves the product quality. Reference may be made to Japanese patent JP2042933 wherein a method for drying of onion is described. The process involves dehydration of finely cut small pieces of onion, pressing the small pieces between a pair of heated drums having the same diameter, peeling the hot pressed small pieces from the drums. The method described here in this process is entirely different from the one adopted in the present invention claimed. The method adopted here is for finely cut onion pieces, which are further dried by conduction heating in a drum dryer. The process doses not use any radiation heating for the dehydration and steam is used for heating the drum surface. This necessitates the installation of a boiler for the process, which involves additional expenditure. Reference may be made to Japanese patent JP2001128614 wherein the method for production of dried of welsh onion is described. The dried grilled Welsh onion is obtained by grilling the raw onion, freezing the grilled onion and then lyophilizing the onion in a frozen state. The above method involves more number of operations such as grilling, freezing and lyophilizing under frozen condition. The freezing operation is an expensive proposition and would increase the processing cost. Also, lyophilizing is a very slow process and it is difficult to have a continuous process with the above operations. Reference may be made to Japanese patent JP59048043 wherein the method for preparation of the dried onion is explained. In the present method onion is cut into strips of 3-4 mm thickness and dried in a hot air dryer. Subsequently, the material is boiled in water for 1-5 h, followed by quick cooling. The material is then dried in a centrifugal separator, frozen and lyophilized or subjected to vacuum drying. This is a tedious process with a number of operations. The process includes operations such as freezing and vacuum drying, which are expensive. Also, when the onion is processed in boiling water for 1-5 h as per the above method, the product may loose its pungency and would be of poor quality in comparison with the present invention. The main object of the present invention is to provide an improved process for retention of pungency during onion dehydration, which obviates the drawbacks of the processes as detailed above. Another object of the present invention is to provide an improved process for the retention of pungency during onion dehydration, which increases the moisture diffusion co-efficient and hence the mass transfer rate in onion, which in turn reduces the processing time. Still another object of the present invention is to provide an improved process for the retention of pungency during onion dehydration, which results in a product with improved color compared to conventional hot air drying. Accordingly the present invention provides a process for the retention of pungency during dehydration of feed and the said process comprising the steps: a) trimming of root and neck portion of the bulbs of the feed; b) peeling of feed followed by slicing; c) characterized in that loading the rings onto the wire mesh conveyor of a combined infrared and hot air heating system; d) setting the processing temperature of heating system in the range of 60-80°C, air velocity in the range of 0.8-2.0 m/s, air temperature in the range of 30-50°C and residence time in the range of 3-6hrs; e) drying the feed till the moisture content of the same reaches in the range of 7-9%, and f) obtaining the treated feed into a moisture free stainless steel collection bin and packing in polyethylene bags for storage. The process flow diagram for the above process is as shown in Figure 1. In an embodiment of the present invention, the onion dehydration may be effected by intermittent infrared radiation with hot air blast. In another embodiment of the present invention, the dehydration may be carried out in combined infrared and hot air heating system with cross flow or through flow (from top or bottom) type convective heating. Still in another embodiment of the present invention, the process is extendable for dehydration of other bulbs such as garlic for which retention of flavor component is essential during dehydration. Still in another embodiment of the present invention, the process can be used for feed having any other shape such as shredding, strip etc. The novelty of the present system is that infrared radiation is applied intermittently and hot air is blasted simultaneously through the material bed to enhance the rate of heat and mass transfer. The rapid heat and mass transfer during dehydration reduces the drying time, which in turn minimizes the loss of flavor. Intermittent radiation with hot air blast reduces the damage to the cell and thereby increases the retention of the flavor component. As infrared radiation heats the material uniformly, the case hardening problem commonly encountered in convective or conductive heating is totally eliminated, which also contributes to the retention of flavor component. The following examples are given by way of illustration of the present invention and should hot be construed to limit the scope of the present invention. Brief description of Table Table 1. Comparison of product quality under different modes of operation Brief description of Figure Figure 1. Schematic diagram of the process for the retention of pungency of onion ring. EXAMPLES Example 1 0.75 kg of commercially available raw onion (Bellary variety) containing 88% moisture was trimmed and peeled. The peeled onion bulbs were cut into 2 mm rings (25 mm diameter). The rings (0.5 kg) were loaded (loading density of 4.5 kg/m2) on to the wire mesh conveyor of combined infrared and hot air heating system. The material was taken inside the heating chamber and dried using only hot air. The heating chamber temperature was set and maintained at 60°C with the help of temperature controller. An air velocity of 2.0 m/s was maintained during the drying process. The drying of onion rings were continued (340 minutes) till the final moisture content of the product was 8.2%. The product was collected in SS 304, moisture free stainless steel vessel and packed immediately in polyethylene pouches. (Figure Removed) Example 2 0.75 kg of commercially available raw onion (Bellary variety) containing 88% moisture was trimmed and peeled. The peeled onion bulbs were cut into 2 mm rings (25 mm diameter). The rings (0.5 kg) were loaded (loading density of 4.5 kg/m2) on to a flat bottom tray of the cross flow tray drier. The heating chamber temperature was set and maintained at 60°C with the help of temperature controller. An air velocity of 0.25 m/s was maintained during the drying process. The drying of onion rings were continued (720 minutes) till the final moisture content of the product was 8.8%. The product was collected in SS 304, moisture free stainless steel vessel and packed immediately in polyethylene pouches. Example 3 0.75 kg of commercially available raw onion (Bellary variety) containing 88% moisture was trimmed and peeled. The peeled onion bulbs were cut into 2 mm rings (25 mm diameter). The rings (0.5 kg) were loaded (loading density of 4.5 kg/m2) on to the wire mesh conveyor of combined infrared and hot air heating system. The material was taken inside the heating chamber and dried using infrared radiation and hot air. The heating chamber temperature was set and maintained at 60°C with the help of temperature controller. An air velocity of 2.0 m/s with temperature at 40°C was maintained during the drying process. The infrared radiation was applied once in 2 minutes for every 60 seconds. Hot air was blast continuously throughout the drying process. The drying of onion rings were continued (220 minutes) till the final moisture content of the product was 8.5%. The product was collected in SS 304, moisture free stainless steel vessel and packed immediately in polyethylene pouches. The overall processing time with infrared heating and hot air heating reduced by 35% and 70% in comparison with though-flow and cross-flow convective heating respectively. The pyruvic acid retention, which is an indicator of flavor component, increased by 54%-58% over convective heating explained in Example 1 and 2. The higher effective diffusivity was obtained with intermittent infrared heating (1.67 x 10" 8) compared to that of convective heating (1.16 xlO8). The rehydration coefficient was higher (0.70) compared to that of through flow (0.62) and cross-flow (0.60) convective heating. Table 1 (Table Removed) The main advantages of the present invention are • The intermittent infrared and hot air drying of onion reduces the processing time over conventional hot air heating. • The product (dehydrated onion) dried with intermittent infrared and hot air heating mode has higher rehydration moisture compared to conventional hot air dried product. • The product (dehydrated onion) dried with intermittent infrared and hot air heating mode has improved color compared to conventional hot air dried product. • The product (dehydrated onion) dried with intermittent infrared and hot air heating mode has higher flavor component compared to conventional hot air dried product. • Simultaneous heating of surface and core with infrared eliminates case hardening in the food material and minimizes the flavor loss. • The developed process is easy to scale up to the commercial level. We claim: 1. A process for the retention of pungency during dehydration of feed such as onion and garlic and the said process comprising the steps: a) trimming of root and neck portion of the bulbs of the feed; b) peeling of feed followed by slicing; c) characterized in that loading the rings onto the wire mesh conveyor of a combined infrared and hot air heating system; d) setting the processing temperature of heating system in the range of 60-80°C, air velocity in the range of 0.8-2.0 m/s, air temperature in the range of 30-50°C and residence time in the range of 3-6hrs; e) drying the feed till the moisture content of the same reaches in the range of 7-9%, and f) obtaining the treated feed into a moisture free stainless steel collection bin and packing in polyethylene bags for storage. 2. A process as claimed in claim 1, wherein the onion is in any form like shredding or strips, preferably rings. 3. A process as claimed in claim 1, wherein the garlic is in the form of cloves. 4. A process as claimed in claim 2, wherein the onion ring is of uniform dimension preferably a ring having dimension 2 to 6 mm thick and 25 mm in diameter. 5. A process as claimed in claim 1, wherein in step (c) the thin layer of feed is exposed to infrared source like quartz, ceramic. 6. A process as claimed in claim 5, wherein the feed is exposed to infrared source radiating electromagnetic energy in the range of 2.4 µm to 3.0 µm, which the food materials absorbs the most and converts into heat energy and any other infrared range. 7. A process as claimed in claim 1, wherein in step (c), the loading density of the feed is 4.5kg/m2. 8. A process as claimed in claim 1, wherein in step (d) the processing temperature is 60°C. 9. A process as claimed in claim 1, wherein in step (d) the air temperature is 40°C. 10. A process as claimed in claim 1, wherein in step (d) the velocity of hot air is preferably in the range of 1.4 - 2.0 m/s. 11. A process for the retention of pungency during dehydration of feed substantially as herein describe with reference to examples accompanying this specification.

Documents:

0759-delnp-2004-abstract.pdf

0759-delnp-2004-claims.pdf

0759-delnp-2004-correspondence-others.pdf

0759-delnp-2004-description (complete).pdf

0759-delnp-2004-form-1.pdf

0759-delnp-2004-form-18.pdf

0759-delnp-2004-form-2.pdf

0759-delnp-2004-form-3.pdf

0759-delnp-2004-form-5.pdf

0759-delnp-2004-pct-199.pdf

759-DELNP-2004-Abstract-(08-05-2009).pdf

759-DELNP-2004-Claims-(08-05-2009).pdf

759-DELNP-2004-Correspondence-Others-(08-05-2009).pdf

759-DELNP-2004-Description (Complete)-(08-05-2009).pdf

759-DELNP-2004-Form-3-(08-05-2009).pdf