The biological material presented in Figure 1 is Capsicum chinense (pepper) fruit.

Fresh red chilli peppers of the Capsicum chinense variety were collected from markets in the city of Brazzaville in the Republic of Congo, including the Total market (MTO) in the Bacongo arrondissement, the Bourreau market (MBO) in the Makélékélé arrondissement and the Tsiémé market (MTS) in the Ouenzé arrondissement. These three (03) markets were chosen because they represent the key markets for the marketing of chillies in Brazzaville. The geolocation of these markets, determined using Garmin GPS, is shown in Table 1 .

Samples of fresh chilli pepper purchased at the market are transported to the laboratory, the chilli pepper are sorted and the putrified ones are removed. The chilli pepper stems were removed and the chilli peppers were washed three (03) times with tap water, then left to drain. After draining, the chilli peppers were ground using an E-Jeff Moulinex and a quantity of cooking salt equivalent to 5% of the weight of the chilli pepper puree was added to each preparation, then the whole was mixed. For each site, 550 g of the mixture was placed in three (03) glass jars with stoppers, sterilized in an oven at 180˚C for 2 hours. The mixture was left to ferment at room temperature for 7 days.

Mass loss was carried out at temperatures of 45˚C, 60˚C and 70˚C using a FALC hot-air oven with temperature 250˚C ± 0.1˚C. Continuous measurement of pepper mass loss through water elimination over time was carried out using a JA500-3N balance with a precision of 500 g ± 0.001 g.

To do this, 15 g of fermented chilli peppers were placed in previously dried and weighed cups, then the whole was placed in a hot-air oven at drying temperature. Drying kinetics were monitored by taking weights every 30 min, and were stopped when the samples had a wet-base water content of at least 10% to 12% which corresponds to equilibrium humidity [11] . Each sample was analyzed in 3 trials. For drying kinetics, water content and reduced water content in dry basis were calculated and given by Equations (1) and (2)

$X=\frac{m-m_s}{m_s}$(1)

where X: water content at time t; m: mass at time t and m_s: equilibrium dry mass

$MR=\frac{M-M_e}{M_0-M_e}$(2)

where MR is the reduced moisture, M is the moisture content at time t, M₀ the initial moisture content and M_e the equilibrium moisture [11] .

As shown in Table 2 , six (06) semi-empirical and empirical models were used to select the best model to describe hot-air oven drying of fermented red chilli pepper. The different mathematical models examined are fitted to the experimental data by applying the linear regression method. Origin Pro 2018 software is used for mathematical modeling of drying.

In these equations, MR represents the reduced water content.

In these equations, MR represents the reduced water content calculated according to the relationship in Equation (2).

The criteria for assessing the smoothing quality of the experimental results are the coefficient of determination (R²), the chi-square (X²) and the root mean square error (RMSE).

These parameters are calculated using Equations (3), (4) and (5) [11] .

$R^2=1-\left[\frac{{{\displaystyle \sum }}_{i=1}^N{\left(M{R}_{pre,i}-M{R}_{\exp ,i}\right)}^2}{{{\displaystyle \sum }}_{i=1}^N{\left(M{R}_{pre,i}-M{R}_{\exp ,i}\right)}^2}\right]$(3)

$X^2=\frac{{{\displaystyle \sum }}_{i=1}^N{\left(M{R}_{\exp ,i}-M{R}_{pre,i}\right)}^2}{N-z}$(4)

$\text{RMSE}={\left[\frac{1}{N}\underset{i=1}{\overset{N}{{\displaystyle \sum }}}{\left(M{R}_{pre,i}-M{R}_{\exp ,i}\right)}^2\right]}^{\frac{1}{2}}$(5)

The coefficient of determination R² is the first criterion for assessing the smoothing quality of experimental results. The model that best describes drying kinetics is the one with the highest R² value and the lowest RMSE and X² values [11] [27] [28] .

The drying kinetics of fermented chilli peppers began with an initial dry-base moisture content of 3.90% ± 0.25% to 4.68% ± 0.14%; 3.81% ± 0.09% to 4.02% ± 0.007% and 4.45% ± 0.13% to 5.42% ± 0.15% respectively for Total, Bourreau and Tsiémé markets.

For the different sites, drying follows a more or less identical pattern, with drying times of 480 min at 45˚C, 240 min at 60˚C and 180 min at 70˚C in the case of the Total market, of 480 min at 45˚C, 240 min at 60˚C and 180 min at 70˚C for the Bourreau market and of 450 min at 45˚C, 210 min at 60˚C and 150 min at 70˚C for Tsiémé market.

The calculated values of the statistical parameters used are shown in Tables 3-5 for the Total, Bourreau and Tsiémé markets respectively. The different models are compared on the basis of R², X² and RMSE values. These values range respectively from 0.94531 to 0.99861, 1.59 × 10⁻⁴ to 7.53 × 10⁻³, 2.38 × 10⁻³ to 9.107 × 10⁻² for Total market, from 0.92376 to 0.99867, 1.55 × 10⁻⁴ to 8, 47 × 10⁻³, 1.65 × 10⁻³ to 1.250 × 10⁻¹ for Tsiémé market and from 0.96134 to 0.99822, 2.20 × 10⁻⁴ to 5.15 × 10⁻³, 1.77 × 10⁻³ to 6.872 × 10⁻² for Bourreau market.

The pattern of high R² values and low X² and RMSE values indicates the good fit of all models to the experimental results.

Continued

For the 3 sites, of the six (06) models studied, the Wang and Singh model gave the highest R² value and the lowest X² and RMSE values for the different temperatures studied. The Wang and Singh model reported the best fit for hot-air oven drying of fermented chilli pepper.

It is followed by the Approach of diffusion model, which gives R² values lower than those of the Wang and Singh model and higher than those of the other models, while X² and RMSE values are higher than those of Wang and Singh and lower than those of the other models. Newton’s model is the one that reports the poorest fit of thin-film drying of fermented chilli pepper for drying in a hot-air oven, with R² values lower than those of the other models and X² and RMSE values higher than those of the other models.

Due to the particularity of fermentation in food safety and preservation, chilli pepper was fermented before being dried. During the fermentation of chilli pepper, the microorganisms responsible for fermentation acidify the environment by producing microbial peptides and organic acids such as lactic acid which makes the environment acidic [21] .

In the case of microbial peptides, these substances have specific antimicrobial activity against many food pathogens, such as Lactobacillus and Lactococcus which produce bacteriocins that inhibit the growth of Listeria, Monocytogenes which are food pathogens.

For organic acids such as lactic acid, vegetables and cereals fermented by lactic acid bacteria mainly of the genus Lactobacillus transform the sugars present in food into lactic acid, the latter lowers the pH of the medium to values of 3.84 ± 0.13 and 4.2 ± 0.01 respectively for fermented corn porridge and Capsicum frutescens fruits preserved in jars [21] [29] .

This acidification of the medium creates a hostile environment for many pathogenic microorganisms such as Salmonella, E. coli, and Listeria which are not acidophilic. This low pH, combined with the absence of oxygen in fermented products, also inhibits the growth of molds and other harmful bacteria. The product resulting from fermentation is, in view of these conditions, a product that can be preserved for a long time in an obvious food safety character.

Time differences in drying kinetics can be influenced by various factors such as temperature, air humidity and air velocity. Temperature is the factor that most influences the rate of water evaporation in products. A low temperature leads to slow drying. This explains the differences observed between drying times. By increasing the drying temperature, water evaporates quickly from the product to the outside, which reduces the drying time.

These results of drying times are close to 300 min, 240 min and 160 min respectively, at temperatures of 55˚C, 60˚C and 70˚C, from those of [11] , who reported on thin-layer drying of fresh peppers The drying times found are lower than those of 16 hours to 33 hours found by [30] on the mathematical modeling of drying in a hot air oven of mango slices (Mangifera indica L.), those of 35 hours on the drying of cocoa beans in the sun [31] and those of 5.5 hours to 8.5 hours found by [32] on the modeling the drying kinetics of Pigeon Pea (Cajanus cajan). These results show that temperature has a significant influence on pepper drying time. An increase in temperature leads to a decrease in product drying time. This confirms that drying speed is a function of the time-temperature pair.

The analysis of the values of the coefficient of determination (R²) revealed values greater than 0.92 [33] . This information thus reflects a good smoothing of the experimental and predicted data in this study.

Of the six (06) models used, the Wang and Singh model is the one that reports a better smoothing, it is followed by the Approach of diffusion model, the Verna model and the Newton model is the one that reports a poor smoothing. This result is close to that of [11] on the thin layer drying of red pepper whose best drying model is that of the diffusion approach and that of verna. The model chosen is different from the logarithmic model chosen in the mathematical modeling of drying in a hot air oven of mango slices (Mangifera indica L.) [30]

These results differ from those of [11] , who reported on thin-layer drying of fresh peppers at temperatures of 55˚C, 60˚C and 70˚C that the best model is the approximate diffusion following by Verna model.