Experiment 1: Optimization of Pre-treatments for Vacuum frying of jackfruit chips
Effects of pre-treatments on quality parameters of vacuum fried jackfruit chips
The quality parameters (water activity, oil content, moisture content, hardness and colour values (L*, a* and b*)) of pre-treated and untreated samples at specific processing condition (100°C, 9kP and 20 min) were compared with consequent atmospheric fried jackfruit chips.
Water activity
Water activity of the pre-treated vacuum fried jackfruit chips significantly changed with different pre-treatments (Fig 1) The water activity of the VF- jackfruit chips was ranged between 0.444 and 0.557 a
w. The water activity of frozen (0.444) pre-treated sample was the least followed by dried (0.480), control (0.487), atmosphere (0.499) and blanched (0.557aw) VF-jackfruit chips.
Perez-Tinoco et al., (2008) represented similar results of a
w values for vacuum fried pineapple chips.
Oil content
The oil uptake of VF-jackfruit chips was significantly affected by the pre-treatments. Oil content was considerably less in vacuum fried jackfruit chips than atmospheric fried jackfruit chips (Fig 2). The highest oil content of 40.25% was noticed in atmospheric chips followed by frozen (38.44%) pre-treated VF-jackfruit chips. During the evaporation of ice crystals during frying, there will be a rapid formation of microstructure pores and this promotes high oil uptake. The result was in agreement with
Ranasalva and Sudheer (2017), who observed a high oil uptake in vacuum fried banana chips pre-treated with freezing. The lowest oil uptake of 33.35% was observed in untreated VF-jackfruit chips. The oil absorption in dried sample (34.25%) was found to be lesser than that of blanched sample (37.76%), this is because the loss of moisture is directly related to oil absorption.
Moyanoa and Pedreschi (2006) observed the lowest oil content in drying pre-treated deep fat fried potato chips. Among the above treatments the untreated sample gave comparatively less oil content and better organoleptic quality.
Moisture content
Moisture content of pre-treated VF- jackfruit chips significantly varied with different pre-treatments (Fig 3). The highest moisture content (0.772%) was observed in frozen sample as well as blanched samples and the least moisture content of 0.472% was observed in dried sample. The highest moisture content in frozen sample was due to uniform removal of moisture during vacuum frying of frozen sample with high temperature difference.
Fan et al., (2006) stated similar trend of moisture reduction in the frozen pre-treated vacuum fried carrot chips. The initial moisture removal of jackfruit slices through drying contributed to low moisture content in the VF-jackfruit chips. Low moisture content was observed in fried potato strips that were air dried prior to frying
(Dehghannya et al., 2015). The moisture content of the control and blanched pre-treated VF-jackfruit chips were 0.501% and 0.735%, respectively. The atmospheric fried jackfruit chips had moisture content of 2.402% which was much higher than frozen pre-treated sample.
Colour values
The colour values of vacuum fried chips showed significant difference with various pre-treatments (Fig 4). The maximum L* of 69.18 was obtained in control sample followed by frozen (51.48) and blanched (41.59) sample. The minimum L* value of 21.12 was observed in atmospheric fried chips. Control jackfruit produced light coloured chips, which is a desirable character. However, dark coloured product was obtained from drying pre-treatment sample. The a* and b* value of vacuum fried jackfruit showed significant variation with pre-treatments. The a* value of VF-jackfruit chips pre-treated with drying had the highest value of 12.9, which indicates the high red colour in the product. The untreated sample had the lowest a* value (2.73).
i.e, the untreated sample had the value almost similar to the fresh sample (2.31). The blanched (11.93) and frozen (12.67) samples also had high a* values. The highest b* value was recorded in frozen pre-treated vacuum fried jack fruit chips (45.05) followed by control (35.35) sample. The blanched and dried pre-treatment samples also had higher b* values, 33.71 and 3.022 respectively. The jackfruit chips fried under atmospheric conditions were turned darker. The change in colour in fried jackfruit chips is due to the interaction of an amine group with a reducing sugar, which is a non-oxidative browning also known as Maillard reaction
(Garayo et al., 2002).
Texture
The textural changes of pre-treated VF-jackfruit chips exhibited significant difference within treatments (Fig 5). The higher hardness value of 2.6 N was observed in VF-jackfruit chips pre-treated with drying. The removal of moisture prior to frying made the product compact and hard in drying pre-treated sample
(Debnath et al., 2012). Fan et al., (2005) reported that lower breaking force correspond to higher crispiness and
Fan et al., (2006) confirmed that crispiness value was higher in case of the drying compared to atmospheric fried and other pre-treatments of vacuum fried carrot chips. The VF jackfruit chips pre-treated with freezing had the lowest hardness value of about 1.65 N, followed by control (1.04N) products. The retention of moisture in the frozen jackfruit slices increased the rate of mass transfer with high oil absorption that lowered crispiness in the product.
Arlai et al., (2012) had also reported that hardness value of vacuum fried okra chips was less when pre-treated with freezing. Hardness value of blanched VF-jackfruit chips was less compared to dried sample (1.76N) and higher than freezed and control VF jackfruit chips.
Optimization of pretreatments for the production of vacuum fried jackfruit chips
Vacuum fried products without any pretreatments (control) gave better quality parameters. Blanched products had a higher water activity, moisture content and oil content. The texture and color of fried products pretreated with drying was not appreciable. Frying done with frozen jackfruit slices had very high oil content even though its water activity was less. The untreated vacuum fried chips had the most desirable characteristics like low water activity, retention of color and texture, low moisture content and oil content. Hence untreated vacuum fried chips (control sample) were only considered for further studies.
Experiment - II
The experiment II was performed for optimization of process parameters
viz, temperature, pressure and time of frying for the production of vacuum fried jackfruit chips. Based on previous reviews, blended rice bran and palm oil in the ratio of 80:20 was selected for vacuum frying. The experiment consists of 8 treatments in 3 replications.
Effects of process parameters on physical properties of vacuum fried jackfruit chips
Optimization of process parameters
viz, temperature, pressure and time of frying was done based on the analysis of quality attributes such as moisture content, water activity, oil content, hardness, colour changes and acrylamide content of vacuum fried jackfruit chips.
Moisture content
The results indicated that frying conditions affected the moisture content (Fig 6). The moisture content ranged from 0.481% to 0.801% in vacuum fried jackfruit chips at different frying parameters. Moisture content of VF-jack fruit chips decreased with increased frying temperature and frying time. This is due to the fact that the more the frying temperature is increased, pressure is lowered and boiling point is reduced. And as a consequence the water in the vacuum fried jackfruit chips will begin to vaporize faster at a higher vacuum level. The low moisture content of 0.481 was observed at frying temperature of 100°C, frying pressure of 9 kPa for a frying time of 20 min. Since the frying was carried out under vacuum which decreased the boiling point of water, the moisture removal was instantaneous without much warm up phase. High moisture content of 0.801% was observed in VF-jackfruit chips at frying temperature of 100°C, frying pressure of 12 kPa and frying time of 18 min. Similar results were observed in the vacuum frying of carrot chips at frying temperature of 118°C (
Garayo and Moreira, 2002). There was significant difference in moisture content of VF-jackfruit chips subjected to different frying conditions. The same phenomena were also observed in vacuum fried carrot chips
(Fan et al., 2005) and for vacuum fried apple chips (
Shyi and Hwang, 2001) and vacuum fried banana chips (
Ruttanadech and Chungcharoen, 2015).
Water activity
The water activity of VF-jackfruit chips with different frying conditions is represented in Fig 7. The minimum and maximum activity value of 0.473 and 0.613 was obtained at frying condition of 100°C, 9 kPa and 20 min (JF3) and 100°C, 12 kPa and 18 min (JF2), respectively. This might be due to high moisture retention at the respective frying temperature, pressure and time. Similar results were observed for vacuum fried carrot chips
(Dueik et al., 2010), vacuum fried shiitake mushroom chips
(Ren et al., 2018). The safe level of water activity for any fried product should be less than 0.6 (
Fontana, 1998).
Oil content
Oil content of vacuum fried jackfruit chips is an important parameter in assessing the consumer accessibility of the product. Oil absorption is a complex phenomenon that happened mostly when the product is removed from the fryer during the cooling stage. The oil content of VF-jackfruit ranged from 28.85 to 34.73% at different frying conditions (Fig 8). The maximum oil content of 34.73% was noted at 110°C, 9 kPa and 20 min (JF7). Also, the minimum oil content of 20.73% (JF3) was observed in VF-jackfruit chips with frying conditions of 100°C, 9 kPa and 20 min.
The oil uptake increased at increased frying temperatures. Absorption of oil was found to be related to the loss of moisture from the jackfruit chips. This may be due to the diffusion gradient created by the loss of moisture through the surface making the surface dry
(Tanushree et al., 2014). The same phenomenon was also observed by
Segovia et al., (2016) for vacuum fried cassava chips at different frying temperature and frying time and
Ranasalva and Sudheer (2017) for vacuum fried banana chips.
Colour values
The colour values of VF-jackfruit chips significantly varied with different process parameters (Fig 9). The L* values of the vacuum fried jackfruit chips ranged from 66.53 to 70.18. The L* values were seen to be inversely proportional to the frying temperature. A higher L* value was observed in VF-jackfruit chips at frying condition of 100°C, 9 kPa and 20 min (JF3). Lower L* value of 66.53 was observed in the VF-jackfruit chips at processing conditions of 110°C, 9 kPa and 20 min (JF7). When frying time was further extended, the L* value decreased at all frying temperatures. Visual observations confirmed the results obtained from colorimeter, since the jackfruit chips fried under atmospheric conditions were darker, more red and yellowish than jackfruit chips under vacuum. The change in color was due to the interaction of an amine group with a reducing sugar, which is a non-oxidative browning reaction also known as Maillard reaction.
The maximum a* value of 3.26 was observed in the VF- jackfruit chips at frying condition of 110°C, 12 kPa and 20 min (JF8) and the minimum a* value of 2.71 was found in the at 100°C, 9 kPa and 20 min (JF8) (Fig 10). In VF-jackfruit chips, green colour was increased with a high negative value at lower frying temperature, whereas at high frying temperature, a* value changed from green to red colour due to browning reaction. The a* value of VF- jackfruit chips significantly varied with different frying conditions.
Higher b* value (35.41) was noted in VF-jackfruit chips at frying condition of 100°C, 9 kPa for 18 min (JF3) and lower b* value (29.46) was noticed at 110°C, 9 kPa for 20 min (Fig 11). A lower value of b* was observed by the increase in frying temperatures. The same phenomenon was also observed, for vacuum fried chicken nugget
(Teruel et al., 2014). The b* value significantly varied with different combinations of frying temperature, pressure and time.
The L*, a* and b* values of fresh ripened jackfruit bulb slices was 75.37, 2.31 and 36.66 respectively. The sample of jackfruit chips fried at a frying temperature of 100°C, a frying pressure of 9kPa and frying time of 20 min showed most precise values of L*(70.18), a*(2.71) and b*(35.41) to fresh sample.
Textural changes
The effect of process parameters on texture in VF-jackfruit chips is highly significant (Fig 12). The hardness value of VF-jackfruit chips increased with frying temperatures. Hardness value of vacuum fried chips ranged between 1.01N to 2.37N at different frying temperature (100°C and 110°C), frying pressure (9 and 12kPa) and frying time (18 and 20 min). The lower hardness value of 1.01 N was noted in VF-jackfruit chips at frying condition of 100°C, 9 kPa for 18 min (JF1) and the higher hardness value of 2.37 N was observed in 110°C, 12 kPa for 20 min (JF8). In case of the VF- jackfruit chips, the hardness value was inversely proportional to the crispiness. The hardness value was high at higher temperature during frying and this is due to loss of moisture. Similar results were observed for increased hardness value of vacuum fried banana chips at 120°C for 14 min
(Yamsaengsung et al., 2011) and vacuum fried potato chips at 144ºC (gara).
Optimization of process parameters for the production of vacuum fried jackfruit chips
Different quality attributes such as moisture content, water activity, oil content, hardness, colour changes and acrylamide content of vacuum fried jackfruit chips were analysed in the study. 8 different combinations of temperature, time and pressure were taken and aforesaid quality attributes were studied. Of these JF3 sample fried at 100°C, 9 kPa and 20 min gave better result in terms of quality.
Changes in the total polar compounds blended oil during vacuum frying
The determination of total polar compounds in frying oil contributes the most important measure of the extent of oxidative deterioration. The oil was evaluated for total polar compounds after its repeated use for several batches of vacuum frying. Total polar compound was determined after every batch of vacuum frying (100°C, 12KPa for 20 min) after cooling. The threshold level of TPC in edible oil was 25-27%. The TPC of blended oil was increased from 9.3% to 14.5% after 30
th batch of vacuum frying, which is well below the threshold limit Fig 13. This made help to recommended for reuse the oil upto 30 times of vacuum frying. The increased in the extent of polar compounds in the oil indicates the formation of compounds such as triacylglycerols, secondary oxidation of oil (
Latha and Nasirullah, 2011).
Cost analysis
From the cost analysis, vacuum fried jackfruit chips was found to be Rs. 617.54/- per kg.