Edited by: Jinkai Zheng, Institute of Food Science and Technology (CAAS), China
Reviewed by: Kin Weng Kong, University of Malaya, Malaysia; Alam Zeb, University of Malakand, Pakistan
This article was submitted to Food Chemistry, a section of the journal Frontiers in Nutrition
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
For the production of healthier fruit snacks, vacuum frying is a promising alternative for atmospheric frying, to reduce the oil content, while maintaining a high nutritional quality. This paper evaluates the effect of ripening stages, frying temperature, and time on the quality of vacuum-fried mango. Unripe mango was dehydrated faster than ripe mango and had a higher hardness after frying at 110 and 120°C. Fat content in fried ripe mango was higher. Total ascorbic acid and β-carotene in both ripening stages were not different, but after frying total ascorbic acid in unripe mango remains higher. A novel image analysis was applied to quantify the color distribution of fried mango. Color changes in unripe mango were more susceptible to temperature and time. Considering all quality parameters, vacuum frying of unripe mango at the optimal condition of 100°C for 20 min is preferred for producing high-quality healthier fruit snacks.
Consumers have a strong desire for fried food products because of their unique flavor–texture combination. However, the increased awareness of consumers toward the relationship between food, nutrition, and health stimulates the food industry to use alternative processing methods complying the demand for healthier snacks. In this paper, we study an alternative frying process to meet these demands by reducing the oil uptake and maintaining a high nutritional value.
Technically deep-frying is heating and dehydrating foods with associated oil uptake by immersing them in an edible fat at 165–190°C (
Deep-frying dries the product, giving it a crust and making it crispy (
Vacuum frying is similar to atmospheric frying but is carried out under reduced pressure below 10 kPa, causing a decrease in the boiling point of water in the fried products (
Several studies on vacuum-fried food have been done for pineapple (
Studies on vacuum-fried mango have been done to compare the vacuum frying technique to atmospheric frying on the oil content, color, texture, total carotenoid content, and the like (
As a climacteric fruit, mango quality is strongly influenced by ripening. During ripening, physiological, biochemical, and molecular changes are initiated in the mango matrix by the autocatalytic production of ethylene and increase in respiration rate. Some of these changes include increased biosynthesis of carotenoids, a decrease in ascorbic acid, conversion of starch into sugars, and the softening of the fruit promoted by the pectinase action on the cell wall. Another influenced quality attribute is color. Color changes in mango result from carotenoid accumulation in the pulp (
The objective of this study was to investigate the effect of ripening stages, frying temperature, and time on the nutritional and physicochemical quality of vacuum-fried mango. The physicochemical quality was characterized by measuring the key parameters moisture and fat content, color and texture. While the nutritional value was assessed by analyzing vitamin C and β-carotene content as key parameters for, respectively, water- and fat-soluble nutrients in mango. The research hypothesis was that quality of vacuum-fried mango chips is affected by ripening stage, frying temperature, and time.
Unripe (stage 2, firmness 68.4–87.9 kg/m2) and ripe (stage 4, firmness 24.4–39.1 kg/m2) mango (
Initial values for firmness and total soluble solid content of unripe and ripe mangoes used for vacuum-frying experiments.
78.25 ± 0.44a | 16.03 ± 0.08a | |
31.91 ± 0.26b | 16.41 ± 0.11b |
Firmness was measured using fruit penetrometer FT327, equipped with an 8-mm tip (Nieuwkoop B.V., the Netherlands). The firmness measurements were done on each peeled mango cheek with three repetitions and were expressed in kg/m2. TSS content was measured three times from juice obtained from mango cheek using a refractometer (HI96801, Hanna Instruments) and was expressed in °Brix. After selection, mangoes were peeled, and the seed was removed and halved. The halved fruits were cut into 4-mm-thick slices with a mandolin (V5 Power, Börner, Germany) to ensure the fast heat penetration to the center of the chips but not collapse during the processing.
Mango slices were vacuum fried in 2-kg batches using a pilot scale industrial vacuum fryer (Florigo Industry B.V., The Netherlands) containing 250 L fresh high oleic sunflower oil. A high oil-to-fruit ratio was needed to diminish temperature drop after the fruit was submerged into the oil. The vacuum fryer was equipped by an automatic basket rotator, two heat exchangers to cool and heat the oil, and an atmospheric spinner to remove surface oil. Some pilot experiments have been carried out to determine the optimal conditions for thickness of mango slices and vacuum frying pressure. Based on these results, 4-mm mango slices were fried at 10 kPa at times and temperatures as listed in
Settings used for vacuum frying mango chips.
90 | 5 | 10 | 15 | 25 | 35 | 50 |
100 | 5 | 10 | 15 | 20 | 27.5 | 35 |
110 | 2.5 | 5 | 10 | 15 | 20 | 25 |
120 | 2.5 | 5 | 7.5 | 10 | 12.5 | 15 |
Two samples of mango slices (1 kg of each of the two ripening stages) were loaded into the vacuum chamber. After 60 s, the desired vacuum pressure was reached, and the basket was submersed into the oil to initiate the frying time. During frying, the basket was rotated back and forth at 17 rpm for 60 s to ensure that the heat and oil were evenly distributed. To stabilize the temperature, a heat exchanger to heat and cool the oil was used. Once the frying was finished, the basket was lifted from the oil and shaken for 20 s inside the vacuum chamber to remove excess of oil. The vacuum chamber was then pressurized, and the vacuum-fried mango was centrifuged to remove surface oil for 60 s at 100 g (MSD-500HD, Eillert B.V., the Netherlands). Then, mango chips were packed in sealed plastic bags and stored at −20°C until further use. All frying experiments were performed in duplicate.
Moisture content of the samples was determined in triplicate per frying experiment with a forced convection oven at 100°C until constant weight and described in % fresh weight. Fat content of the fried mango chips was determined in duplicate per frying experiment with the Soxhlet method using 200 ml petroleum ether 40–60°C after drying overnight and then described in % dry basis (db) (
Texture of the mango chips was measured with a texture analyzer (TA.XT.Plus, Stable Micro Systems, UK) using a three-point bending test according to Da Silva and Moreira (
Since ascorbic acid (AA) easily oxidized into L-dehydroascorbic acid (DHA), vitamin C was calculated as total ascorbic acid (TAA) which sums of AA and DHA. AA was reduced into DHA using TCEP (tris-2-carboxyethyl phosphine) and then calculated together into TAA. The extraction and HPLC analysis was conducted according to the methods of Hernández, Lobo (
The extraction and HPLC analysis of β-carotene was conducted according the methods of Salur-Can, Türkyilmaz (
The color distribution of mango chips was described by a new approach developed specially for this study (
Images of mango chips were taken using a color digital camera (Canon 1000D with Canon EFS 18-55 mm F3.5-5.6 IS lens) mounted on Kaiser RT1 base 25 cm from the product and were placed inside a closed picture chamber. The light used was produced by a 4 × 36 watt 5,400 k 40 Hz fluorescent light mounted at 22° from the sample axis. Color calibration was done using X-Rite ColorChecker Passport and Adobe Lightroom.
An uncompressed picture file (CR2) with image size 3,888 × 2,592 pixel was produced and later converted to another uncompressed file (Exif-tiff 8 bit) at the same resolution by image processing software (Canon Digital Photo Professional, version 3.14.40.0) prior to further analysis. Image background was removed using a quick selection tool from an image processing software (Adobe Photoshop CC 2015). The tiff images were then analyzed using Color Inspector 3D v 2.3(21) within Fiji (
Data analysis was performed using R software by independent
Firmness and TSS content of raw mangoes were measured to determine the required ripeness stages (
Overall, moisture loss during vacuum frying exhibited a classical drying profile (
Effect of frying temperatures, time, and ripening stage on moisture content (M), texture (T), and fat content (F) of mango chips during vacuum frying at 90, 100, 110, and 120°C. Solid lines are unripe mango, and dashed lines are ripe mango. Error bars are standard error. Asterisk shows significant difference between ripening stages (*
At 10 min of frying, the moisture content of unripe mango ranged from 34.4 ± 4.4% at 90°C to 5.2 ± 0.5% at 120°C, while for ripe mango the content was 37.8 ± 2.9% and 14.5 ± 2.4% for the respective temperatures. Even though not significant, this result shows that the moisture of ripe mango was more difficult to evaporate during frying than for unripe mango. This difference could be explained by the structure, soluble solids, and texture differences. Pectin is an important compound influencing those physical characteristics. Pectin is more abundantly present in unripe mango, thereby increasing the water-binding properties (
Moreira (
During vacuum frying, there is an increase in the fat content for mango parts of both ripening stages; however, the fat content of unripe mango showed a sigmoid trend, while ripe mango showed an almost linear increase in fat content during frying (
Fat uptake during vacuum frying is a direct effect of moisture loss. When the mango slices were submerged in hot oil, moisture rapidly evaporated from the surface and allowed oil to adhere to the dry surface (
At most frying conditions, fat content in unripe and ripe mango shows no significant differences, except at the most intense treatments in which the fat content in unripe mango is lower as shown at 90°C for 50 min (
After vacuum frying started, the hardness of fried mango chips initially drops for both ripening stages and at all temperatures and subsequently increases in time. Dueik and Robert (
The hardening process accelerates at higher temperatures. Unripe mango chips fried for 15 min at 90°C had a hardness value of 3.9 ± 0.6 N; this value was at the beginning of the slow phase which increased at a longer frying time. On the other hand, unripe mango chips fried at 120°C for 15 min had a hardness value of 10.6 ± 0.9 N; this value was at the end of the slow phase. Nunes and Moreira (
Overall, there was no significant difference between hardness of unripe and ripe mango after vacuum frying at 90 and 100°C at all-time points. At higher temperatures, the hardening was faster for unripe mango compared to ripe mango. A significant difference (
Vitamin C (AA + DHA) is an important nutritional parameter for fried food products. The raw material used in this study is characterized by a high total ascorbic acid content; raw unripe mango had a higher TAA content of 156.2 ± 6.4 mg /100 g compared to ripe mango (126.6 ± 3.0 mg/100 g). The TAA decrease could be a result of ascorbate peroxidase (APX) activity which uses ascorbates as electron donor to remove hydroxyl radical from the cell that produced during fruit ripening (
As expected, thermal degradation of total ascorbic acid (TAA) increased with increasing frying temperature; a similar pattern was observed in both ripening stages (
Effects of vacuum frying and ripening stages of mango on total ascorbic acid (mg/100 g db) (left) and β-carotene (μg/g db) (right) during vacuum frying. Light bars represent unripe mango; dark bars represent ripe mango. The different frying temperatures also represent the different final frying times; 90°C (50 min); 100°C (35 min); 110°C (25 min); 120°C (15 min). Error bars are standard error. Different letters above the error bars show significant difference between treatments
However, the TAA values remain higher in the unripe mango for all temperatures, although only significantly at 100°C. Frying for 35 min at 100°C retained 65.8 and 59.8% of TAA in unripe and ripe mango. Even at this severe heating, 100 g unripe and ripe vacuum-fried mango is able to provide 114.3 and 84.1% of the recommended daily allowance of vitamin C for adults (90 mg), respectively. This difference shows the importance of the fruit matrix as the container of the ascorbic acid. Davey et al. (
Raw ripe mango had a higher β-carotene content compared to unripe mango, even though not significant (27.2 ± 3.6 and 19.3 ± 5.4 μg/g db, respectively). This result was expected since carotenoid content increases during mango ripening (
There was no significant difference in β-carotene content for each temperature/time combination between the two ripening stages. While in both ripening stages the initial low β-carotene value increases after frying at 90 and 100°C, there is a clear decline in β-carotene content for both ripening stages when temperature is increased (
The possible explanations for the increased ß-carotene concentrations after frying at 90 and 100°C, which were also found in vacuum-fried apricot at 70–90°C (
However, after vacuum frying at 110 and 120°C, the ß-carotene concentrations decreased, which shows the thermal sensitivity of ß-carotene in vacuum frying. Da Silva and Moreira (
The color of fried mango chips is often inhomogeneous with strong local differences, e.g., the occurrence of brown spots in a lighter background. This phenomenon is present in most fried or baked foods. Therefore, measuring the overall color changes, e.g., expressed as L*a*b* values, is not representative for the visual appearance. In many cases, the food matrix and surface are not homogenous and have different structures at micro- and macroscopic scales (
Color distribution in terms of lightness
Unripe (left) and ripe (right) mango slices vacuum fried at 90 (top) and 120°C (bottom) for different times.
The area in levels of lightness decreased gradually upon increasing frying time and temperature. However, a faster trend in lightness reduction was observed for the unripe mango chips, which was most distinct at 110°C and 120°C. The reduction in levels of the light area clearly led to an increase in levels of medium-light and dark areas, also differentiating between the two maturities. Similar results were found by Maity and Bawa (
Similarly, the areas for medium-red and red increased progressively as the frying time and temperature increased, which was also observed by Maity and Bawa (
It was clear that the combination of ripening stage, frying time, and temperature has a substantial influence on the color of the mango chips. Unripe mango fried for a longer time at a higher temperature has a darker and redder surface compared to ripe mango. So, unripe mango seems more susceptible to the temperature–time treatments toward changes in lightness and redness compared to ripe mango. Similar effects were also found in apple, although they were measured as having an average color value of the fried apple surface (
Moisture loss of unripe mango chips was faster than that of ripe mango chips. There was no significant difference between hardness of unripe and ripe mango after vacuum frying at low temperatures (90–100°C), but at higher temperatures (110–120°C), unripe mango had a higher hardness value compared to ripe mango. Vacuum-fried ripe mango had a higher fat content compared to unripe mango. No differences between the ripening stages were found on the degradation of ascorbic acid and β-carotene during frying. Unripe mango is more susceptible to temperature and time toward lightness and redness changes compared to ripe mango. Considering all quality parameters, unripe mango is preferred over ripe mango for vacuum-frying processing. Furthermore, vacuum frying at 100°C for 20 min was sufficient to decrease the moisture content and produce high-hardness chips without adsorbing too much oil, maintain the color without losing too much ascorbic acid, and preserve the β-carotene content.
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.
FA did the study conception and design, acquisition of data, analysis and interpretation of data, and drafting of the manuscript. EG and JV did the study, acquisition of data, analysis and interpretation of data, and drafting of the manuscript. MD did the analysis and interpretation of data, study conception and design, drafting of the manuscript, and critical revision. VF did the drafting of manuscript and critical revision. RV did the study conception and design, drafting of the manuscript, and critical revision. All authors contributed to manuscript revision and read and approved the submitted version.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.