Cite this article as:
Cemal, D., Yildiz, G. (2022) “The effect of drying temperature, cutting types, storage degree and period on physical, chemical and physicochemical properties of red capia pepper”, Latin American Applied Research 52(1), pp 66-72.
Abstract-- This work was undertaken to evaluate the effects of different drying temperatures (50, 60 and 70 oC) and cutting types (ring and cube) on the physical, chemical and physiochemical properties of red capia pepper during storage (14 days) both at room temperature (25 oC) and cold storage (4 oC). Convective drying (CVD) at 50, 60 and 70 oC was applied to obtain dried red capia peppers. The effects of CVD on color values (L*, a*, b*), rehydration ratio, selected chemical properties (dry matter, pH and titratable acidity) and bioactive compounds (total phenolic content and antioxidant capacity) of dried red capia peppers were compared. The samples dried at 60 oC in ring forms under cold storage (6R-CS samples) showed the highest dry matter, pH, titratable acidity and rehydration ratio (87.06%, 5.69, 807.15 mg citric acid/100 g, 6.72%, respectively). The closest L*, a*, b* values to the fresh pepper samples were achieved for 6R-CS samples (L*: 29.87, a*: 12.83, and b*: 17.03). In addition, 6R-CS samples resulted with highest antioxidant capacity and total phenolic content in all storage times.
Keywords-- Bioactive compounds, color, convective drying, red capia pepper, storage
I. INTRODUCTION
Pepper belongs to the Capsicum genus of the Solanaceae family and grows in the United States, South America, Peru, Bolivia, Costa Rica, Mexico and almost all Southern European countries (Kumari, 2012). In addition to being rich in vitamins (especially A and C), minerals, phenolic components and carotene, it also has antioxidant properties (Karaağaç and Balkaya, 2010). Capia pepper is a type of pepper with a long conical structure, meaty, red color and a sweet flavor and has been used as "paste" and "oiliness" for years (Demirel et al., 2012). Although capia pepper is consumed fresh and dried, it is also used in the food industry in the production of canned, tomato paste, pickled peppers, frozen food and sauce. In addition to these, it is also used in the production of antibiotic raw materials, feed materials and dyes (Hekimoğlu and Altındeğer, 2009). As many fruits and vegetables, peppers can also be preserved for a long time by drying process. Drying is one of the oldest methods known for the preservation of food. The purpose of drying is to remove free water from the product and to store the products for a long time. Therefore, the crops can be available in areas besides the harvest season. In addition, the volume and weight of dried products are reduced, making packaging and transportation easier with a low-cost. The most popular method of drying food is the convective drying (Michalska et al., 2016). However, this method causes degradation on taste, color and nutritional compounds in food products (Calin-Sanchez et al., 2014). In this sense, the importance of the temperature applied during the drying process is understood and it is wondered how these variables will have an effect on the quality of the foods. This research, for this reason, has the primarily aim of contributing to the works of the use of convective drying on capia pepper quality. Specifically, the effects of different drying temperatures (50, 60 and 70 oC) and cutting types (ring and cube cutting) on color values (L*, a*, b*), rehydration ratio, and selected chemical properties including dry matter, pH and titratable acidity of dried red capia peppers were compared. In addition, the influence of drying temperature and cutting type on the total phenolic content and antioxidant capacity of red capia pepper during storage (14 days) both at room temperature and cold storage were evaluated.
II. METHODS
A. Sample Preparation and Drying Process
The red capia peppers were obtained at a local market in Iğdır, Turkey and kept at 4 ± 0.5 ºC until the experiments. They were washed to clean the dust, chemical residuals and attached dirt. After removing the excess water from the pepper samples by paper towel, the peppers were prepared in two different forms as a ring with a thickness of 5±0.02 mm and a diameter of 50±0.03 mm and as cubes with a side length of 10±0.07 mm. The initial moisture content of the pepper samples was determined as 83.8 ± 0.54 % by drying at 105 ± 5 °C before reaching the stable weight with oven drying method. Convective drying was applied in a laboratory oven (Memmert UN55, Germany) following the method stated by İzli (2018). The ring and cube shaped capia pepper samples were located in a thin layer. Air velocity was 1 m/s with air temperatures of 50, 60, 70 °C. The drying process was continued until 12% moisture content. About 100 g sample were used for each drying experiment. The experiments were conducted with 3 replications. A short definition of the treatments is tabulated in Table 1.
Table 1. Treatments used in the study
B. Color Measurement
The color changes of fresh and dried capia peppers were measured by a Konica Minolta (CR400, Japan) that is assembled with illuminant D 65- and 8-mm measuring scope in the CIE L* a* b* color scale. Color parameters were described in a 3-dimensional L*, a*, and b* color space, where L* shows the lightness/darkness of the capia peppers, a* demonstrates the redness/greenness, and b* displays the yellowness/blueness (Yildiz, 2021a).
C. Rehydration Ratio, Dry Matter, pH and Titratable Acidity
Rehydration ratio, dry matter, pH, and titratable acidity of convective dried ring and cube shaped capia peppers were determined following the procedures stated by Cemeroğlu (2009). The rehydration ratio (RR) of the dried pepper samples was determined by weighing 2.5 g of CVD pepper samples in distilled water with a ratio of 1:30 (w/w) under 100°C for 10 min. The dry matter of pepper samples was analyzed by drying (Memmert UN55, Germany) at 105 ± 5 oC until the samples arrived at a constant weight. pH values of fresh and dried pepper samples were determined by using pH-meter calibrated previously using pH 4.00 and 7.00 buffer solutions (Consort, multi-parameter analyzer, C3010). Finally, electrometric titration method was applied to determine the titratable acidity of pepper samples.
D. Pepper extract preparation
500 mg of fresh and dried capia peppers were weighed in a test tube and extracted 3 times with 10 mL of methanol: water (80:20, v/v) and shaken for 10 min in each and every step. Later then, the tube was centrifuged at 3500 rpm for 3 min to obtain a clear extract and it was combined in another tube. The analysis of total phenolic content and antioxidant capacity was carried out by using the capia pepper extracts.
E. Total phenolic content (TPC)
The TPC of peppers which is in agreement with the approach stated by İzli and Yildiz (2021) was determined with slight alterations. In brief, a part of extract was filtered through 0.45 µm nylon filter and 1.6 mL of Folin-Ciocalte’s reagent was mixed into 0.4 mL of filtered extract accordingly diluted by methanol: water (80:20, v/v) in a test tube. Contents were mixed by vortexing and left to sit for 5 min. Following that, 1.6 mL of 20% Na2CO3 was put into the mixture and vortexed, the tubes were let to stay at ambient temperature for 90 minutes. Subsequently, the mixture was centrifugated at 3500 rpm for 3 min (Hettich Universal 320R, Germany) and transferred into a cuvette. The analysis was carried out by a UV-VIS spectrophotometer (Mecasys Optizen Pop, Korea) at 765 nm and quantification was figured out by a gallic acid calibration curve, built range from 0 to 30 µg/mL. The findings were expressed as mg GA/100 g of dry weight.
F. Antioxidant capacity (ATC)
ATC of capia peppers was measured based on the DPPH method (Brand-Williams et al., 1995) with small changes. Stock solution of DPPH was arranged via dissolving 10 mg of DPPH in 25 mL of ethanol and diluted with 25 mL of distilled water. Then, the working solution of DPPH was arranged by roundly 400 mL of water: ethanol (1:1, v/v) having absorbance values around 0.75-0.80 at 525 nm. A 0.2 mL of pepper extract was put in a tube and mixed by 3.8 mL of DPPH solution. The tube was put into an orbital shaker and it was mixed for 26 min at 350 rpm in darkness at room temperature. Following centrifugation at 3500 rpm for 3 min, the clear supernatant was obtained, and the absorbance was evaluated at 525 nm using a UV-VIS spectrophotometer. All measurements were performed at 30 min after reacting with extract and DPPH solution. The ATC was expressed as µmol of Trolox per 1 g d.w. of pepper.
G. Statistical data analysis
Statistical analyses were managed using a randomized plots factorial experimental design. The results were analyzed using the JMP (Version 7.0, SAS Institute Inc., Cary, NC, USA). Differences among the mean values were obtained by Fisher’s least significant difference (LSD) test at α = 0.05.
III. RESULTS
A. Color Measurement
The
color changes of fresh and dried capia pepper samples are tabulated in Table 2.
It was observed that the L* value of all the dried samples
decreased significantly compared to the fresh capia pepper (p<0.05). When
compared with the pepper samples dried in cube forms, the samples dried in ring
forms showed significantly higher L* values (Table 2). While
the highest L* values (the closest to the fresh sample) were
found for the samples dried at 60 °C in ring forms (29.87
± 0.63) and cube forms
Table 2. Color values of convective dried ring and cube shaped capia peppers.
a-f: Means superscript with different alphabets in the same column differ significantly (p < 0.05).
(28.75 ± 0.45), the lowest L* value was determined for the samples dried at 70 ºC (Table 2). The lower L* value means darker appearance of the convective‐dried pepper samples at 70 ºC might be because of the non‐enzymatic browning (Maskan, 2000). On the contrary to the L* values, a significant increase in a* values were observed for all dried samples compared to the fresh sample. Among the dried samples, the highest a* value was observed for the samples dried at 70 oC whereas the lowest a* value was found for the samples dried at 60 ºC (Table 2). In brief, the samples dried at 60 °C in ring forms showed the highest L* value, and lowest a* value. The b* values of dried pepper samples was found out to be lower value than that of fresh carrot samples (Table 2). While the highest b* values were observed for capia peppers dried at 50 and 60 ºC, the highest b* value loss was collected for the pepper samples dried at 70 ºC. The preferred colors are those closest to the original color of fresh samples. The capia pepper having higher lightness value can be evaluated as more favourable and marketable products with respect to color quality (Ergunes and Tarhan, 2006). From this point of view, drying at 60 °C in ring forms was suitable since it resulted with a lighter product color compared to other drying temperatures (50 and 70 ºC) and closest color values to the fresh peppers.
B. Rehydration Ratio (RR), Dry Matter, pH and Titratable Acidity (TA)
Dry matter, pH, titratable acidity and rehydration ratio of convective dried ring and cube shaped capia peppers are shown in Table 3. As shown in Table 3, dry matter of convective-dried pepper samples in both ring (87.06%) and cube forms (84.37%) at 60 oC were significantly higher compared to the fresh and other dried samples. On the other hand, the lowest dry matter was obtained for the samples dried at 70 oC (Table 3). All dried pepper samples no matter if the samples dried in ring or cube forms or dried at 50, 60, and 70 oC showed a significant increase on dry matter compared to the fresh pepper samples. In addition, the pepper samples dried in ring forms showed a higher dry matter compared to the samples dried in cube forms. Dried pepper samples showed a significant decrease for pH, and a significant increase for titratable acidity compared to the fresh capia peppers (Table 3). As shown in Table 3, rehydration ratio of CVD pepper samples in ring forms at 60 oC were significantly (p<0.05) higher than fresh capia pepper samples, showing that dried pepper samples in ring forms at 60 oC were easier
Table 3. Dry matter, pH, titratable acidity and rehydration ratio of convective dried ring and cube shaped capia peppers
a-g: Means superscript with different alphabets in the same column differ significantly (p < 0.05).
to recover by rehydration. The possible reason was that better porous structure and higher cell membrane permeability formed in the dried pepper samples in ring forms at 60 oC. From the findings, it is obvious that the water gain is more noticeable in dried pepper samples at 60 oC (6.72 ± 0.11% and 5.99 ± 0.02% in ring and cube forms, respectively) compared to the other capia peppers dried at 50 and 70 oC (Table 3). Similar results were observed in the study of İzli and Yildiz (2021). In addition, CVD capia peppers in ring forms have better rehydration ratio compared to the CVD capia peppers in cube forms.
C. Total Phenolic Content (TPC)
Table 4 shows the effects of drying on TPC of capia pepper samples. Total phenolic content of fresh pepper samples was found as 674.83 ± 1.73 mg GA/100 g d.w for the first day samples. Drying of pepper samples significantly affected the TPC (p<0.05). All CVD pepper samples showed significantly higher TPC compared to the fresh sample (Table 4). An increase on the drying temperature from 60 oC to 70 oC decreased the TPC significantly. As a result of an increase on drying temperature, the reduction in the TPC has also been announced in several works by researchers in pears (Santos et al., 2014) and apple pieces (Vega-Gavez et al., 2012). All dried samples showed a significant reduction on TPC during storage. Dried samples on day 7 showed a significantly lower total phenolic content compared to the first day samples for all treatments. Similarly, dried capia pepper samples on day 14 showed a significantly lower total phenolic content compared to the seventh day samples for all treatments. The reduction on TPC during drying period could be related to the organization of polyphenolics with other compounds (i.e., protein) and/or the differences in the physiochemical occurrence of polyphenols which could not be identified or extracted. Capia pepper samples dried in ring forms showed significantly higher TPC compared to the dried pepper samples in cube forms. In addition, preserving the dried samples at cold storage rather than room temperature leads to significantly higher TPC (Table 4). All in all, if all the factors and treatments are considered, it can be easily said that the capia pepper samples dried at 60 oC in ring forms and stored at cold storage (6R-CS samples) showed the highest TPC for all storage times. The effects of drying methods on the phenolic substances of foods were studied previously. In some works, it was reported that thermal process is very suitable to increase the phenolic content in several food products including dry raisins (Carranza-Concha et al., 2012) and apricots (Sultana et al., 2012). On the other hand, while some studies (Zanoelo et al., 2006; Sultana et al., 2012) showed that total phenolic substances decreased during heat application, some of other studies (Dewanto et al., 2002) pointed out that no notable differences. So, the effects of drying methods on the phenolic substances from different food products might not produce the same and/or similar results. By taking into account of the findings, drying process has changeable impacts on the phenolic substances. The physical and chemical reasons in the nutritional and functional characteristics of dried food products are still continue to be researched. The highest TPC observed in the dried pepper samples at 60 oC could be as a result of more cell degradation and rupture, so those can lead to more phenolic substances to be released. Moreover, this observation was probably due to exposing dried pepper samples at 60 oC to less thermal effect compared to the pepper samples dried at 70 oC.
D. Antioxidant Capacity (ATC)
The differences in the ATC of the pepper samples obtained by different drying application is shown in Table 4. The ATC in the fresh pepper samples was determined as 4183.24 ± 0.12 μmol TE/g d.w. A significant decrease was observed in the ATC of the pepper samples for all drying conditions (Table 4). Several researchers observed a decrease in ATC after drying process (Wojdylo et al., 2009; Sultana et al., 2012; Santos et al., 2014) including strawberries (Wojdylo et al., 2009), pepino (Di Scala et al., 2011) and apple pieces (Sultana et al., 2012). The decomposition of antioxidant compounds at drying process is the reason of this reduction. While the highest ATC was obtained for the pepper samples dried at 60 oC, the lowest ATC was found for the pepper samples dried at 70 oC. Compared to the pepper samples dried in cube forms, the pepper samples dried in ring forms showed significantly higher ATC (Table 4). The capia pepper samples dried at 50 oC showed significantly lower ATC compared to the pepper samples dried at 60 oC. The findings showed that drying achieved at lower temperature in convective drying, which results in longer drying periods, may be the reason of more decrease in the ATC. In addition, all dried pepper samples on first day showed significantly higher ATC compared to the other storage times (days 7 and 14). There might be a synergetic or antagonistic relationship between the antioxidant compounds and other substances (Di Scala et al., 2011). In several research, it was announced that there is a positive relationship between a TPC and ATC in many fruits and vegetables, for instance apricot (Sultana et al., 2012), red pepper (Zhou et al., 2016), pomelo (Yildiz and Izli, 2019a), pumpkin (İzli et al., 2021), quince (Yildiz and Izli, 2019b; İzli and Yildiz, 2021), pear (Yildiz, 2021a; Yildiz, 2021b). On the other hand, the effects of drying on ATC of different food products were conflicting because of different variables such as drying methods and antioxidant determination methodology in addition to
Table 4. The effects of different drying treatments on the total phenolic content and antioxidant capacity of red capia pepper samples
a-k Treatment means showed the effect of
different treatments for the same day are not significantly different (p
0.05).
x-z Treatment
means showed the effect of storage times for the same treatment are not
significantly different (p0.05).
antagonistic or synergistic effects between antioxidants or with other compounds.
IV. CONCLUSIONS
In present study, the impacts of convective drying on color values, rehydration ratio, selected chemical properties including dry matter, pH and titratable acidity and bioactive compounds (TPC and ATC) of dried red capia peppers were compared. A significant development in the physical and chemical properties of ring-shaped convective-dried pepper samples at 60 oC was achieved. The convective-dried capia pepper samples at 60 oC in ring forms and kept at cold storage showed a higher retention of bioactive compounds including total phenolic content and antioxidant capacity during storage. By taking effects of different drying conditions and factors (drying temperature, cutting type and storage degree) on the quality retention of the dried pepper samples into account, the most suitable drying temperature, cutting type and storage degree were determined as 60 oC, ring forms, and cold storage, respectively. The results from this study are significant for the processing of dried pepper samples with enhanced color and bioactive compounds to obtain a high-quality product by optimizing the conditions.
ACKNOWLEDGEMENT
This work was supported by Research Fund of Iğdır University. Project Number: UBY0621Y22.
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Received: June 27, 2021
Sent to Subject Editor: August 2, 2021
Accepted: October 12, 2021
Recommended by Subject Editor Maria Laura Foresti