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Research Article

Different drying temperatures modulate chemical and antioxidant properties of mandai cempedak (Artocarpus integer)

[version 1; peer review: 1 approved, 1 approved with reservations]
PUBLISHED 26 Oct 2018
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This article is included in the ICTROPS 2018 collection.

Abstract

Background: Mandai, the fermented inner skin of cempedak (Artocarpus integer), may have further use as industrial ingredient while maintaining its antioxidative capacity. To promote fermentation, Lactobacillus casei was induced as the starter culture. This research was carried out (i) to investigate the effect of temperature on yield, chemical properties, and antioxidant activity of starter induced fermented mandai powder, (ii) to find the best drying temperature for the powder, and (iii) to find correlations between phenolic contents and antioxidant activity of the powder.
Methods: The drying temperature was used as the variable, and was set at 45, 50, and 55°C at a fixed duration of 18 hours. The control was spontaneously fermented mandai dried at 50°C for 18 hours. Total phenolic content (TPC), hydrolyzed tannic content (HTC), and total flavonoid content (TFC) were spectrophotometrically measured, expressed gallic acid (GAE), tannic acid (TAE), and catechin (CAE) equivalents. Antioxidant capacity was measured by DPPH assay. 
Results: The best mandai powder had total phenolic content of 348.8±55.6 mg GAE kg-1, HTC of 143.8±9.3 mg TAE kg-1, TFC of 17.5±1.3 mg CAE kg-1, antioxidant activity (IC50) of 56.96 ppm, ash content of 4.0±0.7%, pH value of 5.0±0.8, and yield of 9.3±0.8%. There was a strong correlation between TPC, HTC, TFC, and the antioxidant activity.
Conclusions: Drying temperature affected all observed parameters but not ash and pH. Temperature of 45°C emerged as the best treatment to produce mandai powder from L. casei-inoculated mandai cempedak fermentation. The antioxidant activity of mandai cempedak was contributed by the phenolic components.

Keywords

Antioxidant activity, Artocarpus integer, drying temperature, polyphenols

Introduction

In South and East Kalimantan, Indonesia, people historically consume the lactic acid bacteria (LAB)-fermented inner skin of cempedak (Artocarpus integer), traditionally termed dami or mandai1. The inner skin of cempedak can be used in functional food production, which may partly reduce agricultural waste2. Mandai may contain phenolics, flavonoids, tannins, and antioxidant activity.

The unfermented cempedak inner skin (Artocarpus integer) contains bioactive components such as phenolics, flavonoids and carotenoids3. It has antioxidant activity that is potentially higher than the flesh and seeds of cempedak. Mandai with L. casei as the starter had better antimicrobial activity against S. aureus and E. coli in comparison to spontaneous (L. plantarum) mandai4. In addition, mandai may function as a probiotic food5. While maintaining its antioxidative capacity, fermented mandai may have further use as industrial ingredient primarily as an exotic tropical flavor and a flavor enhancer.

Mandai powder is produced through drying process. To produce good quality mandai powder, the right drying temperature is required. Drying at the correct temperature minimizes antioxidant damage, implicating the ability to reduce free radicals will be higher, as seen in sinom beverage powder6, and cumari peppers7.

This research aims (i) to measure chemical and antioxidant properties of L. casei-fermented mandai at 45, 50, 55°C of drying temperature with constant time of drying at 18 hours, which the results are then compared with spontaneously fermented mandai and dried at 50°C for 18 hours; (ii) to find the best drying temperature on starter induced fermented mandai powder; and (iii) to find correlations between phenolic contents and antioxidant activity on starter induced fermented mandai powder.

Methods

Producing mandai powder from the inner skin of cempedak

Cempedak was peeled and separated from its husk and flesh, then washed and cut into pieces. The pieces of cempedak inner skin were boiled at 100°C for 5 minutes to remove the sap. The sample was drained and then boiled once more in a sealed container at 100°C for 5 minutes to soften the texture. The sample was then cooled until the temperature was less than 40°C. L. casei strain Shirota isolated from Yakult® as starter culture were inoculated at the concentration of 2% (v/v). For spontaneous fermentation, the mandai was directly stored without inoculation. The spontaneous and inoculated mandai were stored for 2 weeks at temperature of 8±2°C to allow slow fermentation to occur. After incubation, mandai was drained and blended. The puree of mandai then was dried for 18 hours at the appropriate temperature treatment, then ground and screened with an 80-mesh sieve. All reagents and corresponding suppliers are listed in Supplementary File 1.

Extraction of mandai powder

For the analysis of TPC, HTC, TFC, and antioxidant activity, 20 g mandai powder was dissolved in 60 ml 95% ethanol (SmartLab cat no. A1035, Indonesia) and macerated for 24 hours. Mandai was filtered through filter paper (Whatmann no. 4) and the liquid extract was dried at 50°C for 16 hours.

Yield, ash, and pH

Yield was measured as the ratio of mandai powder to initial mandai cempedak (w/w), while ash contents were measured as descibed8. About 2 g of sample was diluted with distilled water to a volume of 20 ml. This mixture was homogenized and allowed to soak for 15 minutes before the pH was measured.

Phenolic content and antioxidant activity measurement

TPC was estimated by the Folin-Ciocalteu assay and expressed as gallic acid equivalents (GAE), as described previously9,10. HTC was estimated by the Folin-Ciocalteu assay and expressed in mg kg-1 tannic acid equivalent (TAE), as described11. TFC was estimated using the aluminum chloride (AlCl3) method and expressed in mg kg-1 catechin equivalent (CAE), as described12. The antioxidant activity was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, as described13. All standards were purchased from Sigma-Aldrich.

Statistical analysis

Data in Table 1 except IC50 of antioxidant activity were subjected to analysis of variance (ANOVA) and the significance of the difference between the averages was determined by Fisher’s least significant difference (at α =5%, analyzed with GraphPad Prism version 6.0. Values were expressed in average ± standard deviation (SD). IC50 of antioxidant activity was produced by employing the non-linear fit of one-phase association method with GraphPad Prism version 6.0. Pearson correlation analysis was performed with Microsoft Excel 2016.

Table 1. Yield, ash, pH phenolic contents and antioxidant activity of powdered mandai cempedak.

Temperature (°C)Yield (%)Ash (%)pHTPC
(GAE mg/kg)
HTC
(TAE mg/kg)
TFC
(CAE mg/kg)
Antioxidant Activity
(IC50 in mg/kg)
AverageR-square
459.3±0.8ac4.0±0.7 5.0±0.8 358.8±55.6a143.8±9.3a17.5±1.3a56.960.93
509.1±0.8ac3.5±0.8 4.8±0.8 236.3±12.4c96.5±8.7c5.1±1.8cb66.760.96
559.1±0.6bc3.0±0.7 4.5±0.5 199.2±13.4c67.3±6.6d1.6±1.0d84.740.96
control9.3±0.6c3.2±0.9 5.3±0.2 275.1±14.2b115.3±8.2b7.0±1.3b136.780.97

Yield, ash, pH, total phenolic content (TPC), hydrolyzed tannin content (HTC), total flavonoid content (TFC) are presented in average ± standard deviation.

Letters after the numbers indicate the least significant difference at α=5%

Results

Yield, ash, and pH

The yield of mandai powder at drying temperatures of 45 and 50°C did not differ significantly. However, the yield of mandai powder dried at a temperature of 55°C was significantly different to the yield resulting from treatment temperatures of 45 and 50°C (Table 1). The yield of each treatment did not differ significantly with the yield of mandai powder with spontaneous fermented that dried at 50°C (control). A comparison between the ash content of each treatment with control showed no significant difference (Table 1). The pH values of dissolved mandai powder ranged from 4.5±0.5 to 5.3±0.2. The drying temperature did not affect the pH value of the dissolved mandai powder.

TPC, HTC and TFC

The drying temperature significantly affected the TPC of mandai powder. The highest average value of TPC in mandai powder dried at 45°C. In comparison to control, TPC of each treatment was significantly different. The drying temperatures in each treatment resulted in significantly different HTC in comparison to that of control mandai. Drying temperature of 45°C produced higher HTC than that of mandai powder dried at 50°C and 55°C. The drying temperature significantly affected the TFC of mandai powder. The TFC of mandai powder which dried at 45 and 55°C were significantly different from the control, but that of dried at 50°C was not significantly different from control.

Antioxidant activity

Half-maximal inhibitory concentration (IC50) value of DPPH for each treatment was obtained through one phase association equation. The drying temperature significantly affected the antioxidant activity of mandai powder. Control mandai powder extract had the highest IC50 value, while mandai powder extract dried at 45°C had the lowest IC50 value of (Table 2). The TPC, HTC, and TFC have a strong correlation with antioxidant activity. The higher TPC, HTC, and TFC value, the higher antioxidant activity in mandai powder (Table 3).

Table 2. IC50 of antioxidant activity of powdered mandai cempedak.

TreatmentY0PlateauKIC50
(Interpolated)
Vitamin C0103.400.003209.11
45°C089.990.01456.96
50°C091.120.01166.76
55°C091.440.00984.74
Control087.390.006136.78

Y0, (0% inhibition / without extract or Vitamin C); Plateu, maximum peak value; K, inhibition rate constant depended on concentration of Vitamin C or extract; IC50, concentration of Vitamin C or extracts inhibiting DPPH reduction by 50%.

Table 3. Pearson correlation between total phenolic, tannin, flavonoid and antioxidant activity of mandai powder.

VariableR-value
TPCHTCTFC
Antioxidant activity0,7960,9100,783
TPC0,9730,999
HTC0,967

0,01-0,19 very weak correlation; 0,20-0,39 weak correlation; 0,40-0,59 moderate correlation; 0,60-0,79 strong correlation; 0,80-1,00 very strong correlation.

Correlation of TPC, HTC, TFC and antioxidant activity

Based on Pearson correlation analysis, there was a strong correlation between total phenolic content (r = 0.796) and total flavonoid content (r = 0.783) with antioxidant activity. The strongest correlation occurred between total tannin content (r = 0.910) and antioxidant activity in mandai powder.

Dataset 1.All raw data obtained in the present study.
Data include yield, ash weight, pH, and phenolic, tannin and flavonoid contents.

Discussion

Yield, ash and pH

More water in mandai evaporated at higher temperatures. This caused the yield of mandai powder to reduce with increasing drying temperature. A previous report documents that the yield may decrease with increased drying temperatures14. The drying temperature did not affect the ash content of mandai powder. The mineral resources in the spontaneous and L. casei-fermented mandai were equally used by microbes, so it did not have a different effect to ash content.

During mandai fermentation, population of LAB increased until day 14, thus lowering pH1,5. Inferring from previous research, it was deduced that organic acids such as lactic acid and acetic acid were produced to lower the pH and caused more acidic environment on day 12 of fermentation5. The fermentation medium, duration of fermentation, and the use of starter cultures may play a role in the final pH and organic acid contents of LAB-fermented products. The previous research stated that the pH of spontaneously fermented rye dough was higher than the pH of starter-fermented rye dough15. However, cucumber pickle fermented with LAB produced organic acids that were higher than that of spontaneous fermentation16.

TPC, HTC and TFC

TPC of the inner skin of cempedak was at 21.29 mg GAE kg-13. TPC of mandai powder ranged from 199.2±13.4 to 348.8±55.6 mg GAE kg-1, higher than that of unfermented cempedak. Phenolic compounds were sensitive to heat treatment, so that the drying process reduced the TPC17. The TPC of mandai powder dried at 55°C was the lowest value observed when compared to other treatments. The drying process, especially at higher temperature (i.e. 55°C), combined with the long drying time duration (i.e. 18 hours) resulted in loss of antioxidant activity18.

In dry conditions, components in the cell, such as membranes and organelles, clump together, resulting in fewer extracted phenolic compounds14. Drying at 50°C quickly disabled the oxidation of polyphenols. However, the initial oxidation of polyphenols might have occurred prior to drying and led to polyphenol degradation. Phenolic compounds are sensitive, unstable and susceptible to degradation by oxygen and light19. The enzymatic oxidation of polyphenols components is mostly caused by polyphenol oxidase7. Injury to the cell membrane liberates and therefore activates these enzymes, which convert phenolic compounds to quinones.

Phenolic contents are often subjected to heat processing, such as drying, boiling, and steaming19. Environmental factors affecting phenolic concentrations include weather conditions, seasons, and post-harvest conditions20. Phenolic contents are also related to varieties of different fruits, diversity of extraction methods21, and the type of phenolic components in the plant and its location in the cell, as well as the type of solvent and method of extraction22–24.

L. casei may modify the phenolic component, causing a significant difference between TPC of each treatment and control25,26. The type of fermentation and metabolic activity of LAB may play a role on levels of total phenolic in rye dough and bread15 and Moringa oleifera leaf powder27. HTC was inversely correlated with drying temperature. In addition, duration of drying contributes to the loss of tannins28,29. This is consistent with the results in yacon (Polymnia sonchifolia) and coffee leaf tea30,31. Degradation of flavonoid structures is linked to the degree of heat exposure30,32.

Correlation of TPC, HTC, TFC and antioxidant activity

The antioxidant activity of mandai powder was low when compared to the fresh form. Temperature plays a role in retaining antioxidant activity of the powder (Table 2). Temperature had a significant effect on the inhibition of free radicals of DPPH in grass jelly (Premna serratifolia)33. A strong correlation was observed between antioxidant activity and the polyphenol contents of mandai powder. Previous studies have reported strong correlations between TPC, HTC, TFC and antioxidant activity34,35. Phenolic chemical structure has a role in the inhibition of free radicals, largely depending on the number and position of the hydrogen donation from the hydroxyl group to the aromatic ring of the phenol molecules36.

Conclusions

Drying temperature affected total phenolic, tannin and flavonoid contents, antioxidant activity, and yield but did not affect ash content and pH of starter induced fermented mandai powder. Mandai powder dried at 45°C for 18 hours emerged as the best treatment, with a TPC of 358.8±55.6 mg GAE kg-1 dry sample, HTC of 143.8±9.3 mg TAE kg-1 dry sample, TFC of 17.5±1.3 mg CAE kg-1 dry sample, antioxidant activity (IC50) of 56.96 ppm, ash content of 4.0±0.7%, pH value of 5.0±0.8, and yield of 9.3±0.8%. The strongest correlation was shown between HTC and IC50 of antioxidant activity on starter induced fermented mandai powder. The antioxidant activity of mandai cempedak was contributed by the phenolic components.

Data availability

Dataset 1. All raw data obtained in the present study. Data include yield, ash weight, pH, and phenolic, tannin and flavonoid contents. DOI: https://doi.org/10.5256/f1000research.16617.d22191137.

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Rahmadi A, Sabarina Y and Agustin S. Different drying temperatures modulate chemical and antioxidant properties of mandai cempedak (Artocarpus integer) [version 1; peer review: 1 approved, 1 approved with reservations]. F1000Research 2018, 7:1706 (https://doi.org/10.12688/f1000research.16617.1)
NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.
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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
Version 1
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PUBLISHED 26 Oct 2018
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Reviewer Report 11 Feb 2019
Francisc Vasile Dulf, Faculty of Agriculture, Department of Environmental and Plant Protection, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Cluj-Napoca, Romania 
Approved
VIEWS 3
This paper aims: to measure chemical and antioxidant properties of L. casei-fermented mandai at different drying temperatures with constant time of drying at 18 hours. The results are then compared with spontaneously fermented mandai and dried at 50°C for 18 ... Continue reading
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Dulf FV. Reviewer Report For: Different drying temperatures modulate chemical and antioxidant properties of mandai cempedak (Artocarpus integer) [version 1; peer review: 1 approved, 1 approved with reservations]. F1000Research 2018, 7:1706 (https://doi.org/10.5256/f1000research.18160.r42635)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
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Reviewer Report 13 Dec 2018
Syed Ziaur Rahman, Department of Pharmacology & Deputy Medical Superintendent, Jawaharlal Nehru Medical College Hospital, Aligarh Muslim University, Aligarh, Uttar Pradesh, India;  Ibn Sina Academy of Medieval Medicine & Science, Aligarh, India 
Mohd Ashraf Alam, Department of Pharmacology , Jawaharlal Nehru Medical College Hospital, Aligarh Muslim University, Aligarh, Uttar Pradesh, India 
Approved with Reservations
VIEWS 15
It is very interesting research which has tried to explore the use of Mandai as industrial ingredient while maintaining its antioxidant activity. However, there are some suggestions and queries, which needs to be corrected along with grammatical errors.
  ... Continue reading
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Rahman SZ and Alam MA. Reviewer Report For: Different drying temperatures modulate chemical and antioxidant properties of mandai cempedak (Artocarpus integer) [version 1; peer review: 1 approved, 1 approved with reservations]. F1000Research 2018, 7:1706 (https://doi.org/10.5256/f1000research.18160.r41487)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 10 Mar 2020
    anton rahmadi, Department of Agricultural Products Technology, Mulawarman University, Samarinda, 75119, Indonesia
    10 Mar 2020
    Author Response
    Addressing Comment (1)
    Abstract structure is assigned by the journal already.

    Addressing Comment (2)
    Two consecutive boilings at 100°C for 5 minutes assisted removal of sap in the inner ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 10 Mar 2020
    anton rahmadi, Department of Agricultural Products Technology, Mulawarman University, Samarinda, 75119, Indonesia
    10 Mar 2020
    Author Response
    Addressing Comment (1)
    Abstract structure is assigned by the journal already.

    Addressing Comment (2)
    Two consecutive boilings at 100°C for 5 minutes assisted removal of sap in the inner ... Continue reading

Comments on this article Comments (0)

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Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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