Effect of pre-treatments and drying methods on quality attributes of sweet bell-pepper (Capsicum annum) powder

Post-harvest profile, processing and value addition of dried red chillies (Capsicum annum L.)

Chilli has dominated and retained an important place amongst the spices worldwide. They are dried ripe fruits intuitively consumed as a spice, condiment, culinary, and medicinal purposes. The global consumption pattern is intriguing because of the inherent pungency, aroma, taste, spicy flavour, and therapeutic properties. Predominantly, the colour and pungency decide the quality features and are actively responsible for organized marketing and trade of the dried chillies. India is one of the leading producers and exporters of chilli. The chemical composition of the chillies varies substantially with agro-climatic zones and post-harvest management strategies. The quantum of post-harvest loss of 25-35% hampers the farmer's income and affects the wholesale/retail marketing. This review paper is intended to provide a deep insight into the advancements in various post-harvest unit operations of dried red chillies. A detailed overview of post-harvest operations (drying, grading, destalking, packaging, storage) and processing techniques for value-added products (chilli powder, dried flakes, seeds, oleoresin) is discussed in this paper. The presented information will help the researchers and the industry personnel engaged in the post-harvest processing and value addition of dried red chillies.

Graphical abstract

A simple and reliable QSPR model for prediction of chromatography retention indices of volatile organic compounds in peppers

Worldwide, various types of pepper are used in food as an additive due to their unique pungency, aroma, taste, and color. This spice is valued for its pungency contributed by the alkaloid piperine and aroma attributed to volatile essential oils. The essential oils are composed of volatile organic compounds (VOCs) in different concentrations and ratios. In chromatography, the identification of compounds is done by comparing obtained peaks with a reference standard. However, there are cases where reference standards are either unavailable or the chemical information of VOCs is not documented in reference libraries. To overcome these limitations, theoretical methodologies are applied to estimate the retention indices (RIs) of new VOCs. The aim of the present work is to develop a reliable QSPR model for the RIs of 273 identified VOCs of different types of pepper. Experimental retention indices were measured using comprehensive two-dimensional gas chromatography coupled to quadrupole mass spectrometry (GC × GC/qMS) using a coupled BPX5 and BP20 column system. The inbuilt Monte Carlo algorithm of CORAL software is used to generate QSPR models using the hybrid optimal descriptor extracted from a combination of SMILES and HFG (hydrogen-filled graph). The whole dataset of 273 VOCs is used to make ten splits, each of which is further divided into four sets: active training, passive training, calibration, and validation. The balance of correlation method with four target functions i.e. TF0 (WIIC = WCII = 0), TF1 (WIIC = 0.5 & WCII = 0), TF2 (WIIC = 0 & WCII = 0.3) and TF3 (WIIC = 0.5 & WCII = 0.3) is used. The results of the statistical parameters of each target function are compared with each other. The simultaneous application of the index of ideality of correlation (IIC) and correlation intensity index (CII) improves the predictive potential of the model. The best model is judged on the basis of the numerical value of R2 of the validation set. The statistical result of the best model for the validation set of split 6 computed with TF3 (WIIC = 0.5 & WCII = 0.3) is R2 = 0.9308, CCC = 0.9588, IIC = 0.7704, CII = 0.9549, Q2 = 0.9281 and RMSE = 0.544. The promoters of increase/decrease for RI are also extracted using the best model (split 6). Moreover, the proposed model was used for an external validation set.

Photochemical advanced oxidative process treatment effect on the pesticide residues reduction and quality changes in dried red peppers

Pesticide residues in crops are widely monitored, and the residue reduction techniques at the post-harvest stage are important to maintain food safety. In dried crops, pesticide residues can be concentrated after dehydration, which increases concerns regarding residue risk. Therefore, the residue reduction effects of ultraviolet (UV), ozone, and photochemical advanced oxidative process (pAOP) were investigated for dried peppers at the post-harvest stage. UV₂₅₄ treatment reduced 59.7% of the residue concentration on average, while UV₃₆₀ showed a reduction of only 13.3% under 9.6 W m^-2 of UV exposure for 24 h. Gaseous ozone treatments reduced the residue concentrations up to 57.9% on average. In contrast, the pAOP treatment reduced the concentration up to 97% and was superior to UV or ozone treatment alone. Increased drying temperature under pAOP condition resulted in higher reduction ratios at 40-80 °C. The pAOP conditions with 12 and 24 µmol/mol of ozone and UV₂₅₄ irradiation for 24-48 h reduced the residue concentrations to 39-67%. Particularly, difenoconazole, fludioxonil, imidacloprid, and thiamethoxam residue concentrations were drastically reduced by over 50% under 12 µmol/mol ozone of the pAOP condition, while carbendazim, fluquinconazole, and pyrimethanil were relatively stable and their concentrations reduced below 50% under 24 µmol/mol ozone of the pAOP treatment. Various drying-related quality parameters of drying peppers such as water-soluble color, capsanthin, capsaicinoids, acid value, peroxide value, and thiobarbituric acid value were slightly altered, but not significantly, under 12 µmol/mol ozone of the pAOP condition, while the peroxide value was significantly altered under the higher ozone conditions. Therefore, pAOP treatment combined with gaseous ozone can be used for reducing residual pesticides in peppers without greatly reducing quality.

Osmo-air drying of banana slices: multivariate analysis, process optimization and product quality characterization

In the present work, osmotic dehydration (OD) was applied as a pretreatment to hot air drying of banana slices and the effect of OD parameters on mass transfer characteristics, color profile was analysed. Principal component analysis (PCA) of OD process revealed that solid gain, weight reduction, water loss and total soluble solids were positively correlated with each other but were found to be negatively correlated with moisture content (MC) of sample. Response surface methodology was used for optimizing the OD of banana slices and and the optimum conditions were 61.26°Brix sucrose concentration at 50 °C for 6 h, resulting in moisture reduction from 75 to 49.78%. PCA-biplot of osmo-air drying (OAD) process showed the association among response parameters, which further revealed a positive correlation of MC with bioactive components. Additionally, OAD samples were also studied for microstructure and Fourier Transform Infra-red analysis. Addition of calcium lactate to sucrose solution resulted in preserving the firmness and bioactive components during osmosis, in addition to fortifying the sample with calcium. The present study provides new possibilities for food industries in preserving the ripe banana and developing calcium fortified functional food products.

Convection Drying Influence on Thermo-Physical Properties, Bioactive Substances, Color and Texture Profile of Red Pepper (Capsicum Spp)

This work aimed to study the effect of convection drying on bioactive substances and on the texture profile of red pepper. Four mathematical models were used to model the drying kinetics, as a function of the temperature and the thickness of slices. These models are largely in agreement with experimental data. Effective diffusivity, Arrhenius constant, activation energy and thermal properties changed with temperature of dry process. The two varieties of pepper used in this work demonstrated a very high degree of spiciness (144799.37-160899.37 SU). This property is related to the high contents of capsaicin (39.60-44.01 mg/g) and dihydrocapsaicin (32.33-35.95 mg/g). Our results revealed that brittleness, hardness 1 and 2, firmness, chewiness, gumminess appearance and Young’s modulus are very important attributes in determining the textural profile of dried red pepper. Also, drying causes a strong degradation of natural pigments of red pepper and consequently decreases attractiveness of the texture profile. To avoid that, red pepper should be pretreated before the application of hot air drying.

Pulsed Vacuum Drying of Pepper (Capsicum annuum L.): Effect of High-Humidity Hot Air Impingement Blanching Pretreatment on Drying Kinetics and Quality Attributes

With a high moisture content, fresh peppers are perishable and rot easily. Drying is essential for shelf-life extension. The natural thin wax layer on the pepper surface hinders moisture transfer. Traditionally, chemical dipping or mechanical pricking is used to remove this wax layer. However, in chemical dipping, chemical residues can trigger food-safety issues, while the low efficiency of mechanical pricking hinders its industrial application. Feasible pretreatment methods are advantageous for industrial use. Here, an emerging pretreatment technique (high-humidity hot-air impingement blanching, HHAIB) was used for peppers before drying and its effects on drying characteristics, microstructure, and polyphenol oxidase (PPO) activity were explored. The impact of drying temperature on color parameters and red pigment content of pulsed-vacuum-dried peppers was also evaluated. PPO activity was reduced to less than 20% after blanching at 110 °C for 60 s. HHAIB reduced drying time and PPO activity and promoted chemical-substance release. Effective water diffusivity was highest (5.01 × 10-10 m2/s) after blanching at 110 °C for 90 s, and the brightness value and red pigment content were highest (9.94 g/kg) at 70 °C. HHAIB and pulsed vacuum drying are promising pretreatment and drying methods for enhancing the drying rate and quality of red peppers.

Influence of Pre-Drying Treatments on Physico-Chemical and Phytochemical Potential of Dried mahua Flowers

Mahua (Madhuca longifolia) flowers are boon for the local tribes of India and have been successfully utilized traditionally for the value addition, and are very prone for microbial spoilage. Local folks utilized malpractices of drying which deteriorates the quality attributes of the mahua flowers and ultimately fails to fetch a good price in the market. Present investigation was led to consider the impact of different pre-treatments i.e., blanching time; and dip of potassium meta-bisulfite (KMS) and citric acid (CA) on the physico-chemical and phytochemical potential of dried mahua flowers using response surface methodology (RSM). Maximum physico-chemical and phytochemicals attributes were observed under optimum conditions i.e., a blanching of 4.1 min followed by dipping in solution having 1285 ppm KMS and 0.77% citric acid. Qualitative analysis through Fourier transform infrared spectroscopy (FTIR) supported the findings. Sugar and phytochemical profiling by high performance liquid chromatography (HPLC) proved the significant effect of each variable. No specific cluster formation was observed during cluster analysis of whole data indicating the significant and equal effect of all variable on the quality of dried mahua flowers. The optimized conditions will definitely help the local processors as well as the industrialist to maintain the quality attributes of the dried mahua.

The effect of different drying techniques and microwave finish drying on the powder properties of the red pepper powder (Capsicum annuum L.)

The objective of this study was to investigate the effects of different drying processes (microwave, freeze, convective hot air, and vacuum drying) and microwave finish drying (FD + MD and CD + MD) on the physical and powder properties of the red pepper powder. The effect of moisture content on the powder properties and the relationship between microwave output power or drying temperature and physical and powder properties were also determined by using most common mathematical models (linear, power, logarithmic, and quadratic). Results showed that an increase in both microwave output power and temperature (for CD and VD) generally resulted in a decrease in drying time, moisture content, and chroma and an increase in bulk and tapped density values. The drying time, moisture content, and water activity values can be significantly decreased, whereas, the color values can be significantly increased by combining FD and CD with microwave finish drying (P < 0.05). The moisture content (y = - 1.94 ln(x) + 7.6455, R² = 0.9905), bulk (y = 54.224 ln(x) + 153.71, R² = 0.9705), tapped (y = 61.7 ln(x) + 225.6, R² = 0.9994) and particle densities (y = - 327.4 ln(x) + 2260.5, R² = 0.9966), and porosity (y = - 3.778 ln(x) + 89.806, R² = 0.9586) values followed a logarithmic trend depending on the increase in the convective hot air drying temperature. The inverse relationship was observed between the moisture content, bulk and tapped densities of the red pepper powders.

Effect of ultrasound and chemical pretreatment on drying characteristics and quality attributes of hot air dried pineapple slices

Drying of food materials is a time consuming activity making the process cost and energy intensive and hence, several pretreatments are used to improve the drying rate. The present study aims to study the effect of potassium metabisulphite (KMS solution, 0.25% w/v) and ultrasound (20 and 30 min) pretreatment on hot air drying characteristics and quality of pineapple slices. The results indicated that pretreated samples provided higher drying rate, enhanced moisture diffusivity, brighter color and lower hardness than that of untreated dried sample. It was observed that KMS and ultrasound pretreatment for 20 and 30 min reduced the drying time by 23.8%, 19% and 14.3%, respectively. Further, ten thin layer drying models were applied to the experimental drying data and logarithmic model was best fitted to explain the drying behavior of pretreated and untreated samples. Additionally, the effect of shrinkage on moisture transfer mechanism was also studied. Results highlighted that instantaneous moisture diffusivity was increased during drying while shrinkage was not accounted. However, shrinkage consideration reduced the average moisture diffusivity values by 72-83%. Overall color change (13.95 ± 0.92) and browning index (36.02 ± 2.45) were found to be lowest in ultrasound (30 min) pretreated dried sample, highlighting better color stability. Scanning electron microscopy presented noticeable effects of pretreatment on alterations of microstructure of pineapple slices. It can be interpreted that KMS pretreatment was found to be more effective for improvement of drying characteristics of pineapple slices as compared to ultrasound pretreatment.

Evaluation of the content of pigments and total sugars in ground sweet paprika

The aim of this research was to evaluate and compare the content of pigments and total sugars in raw materials of both the domestic as well as foreign origin that are used in the production of sweet ground pepper. The tests included two samples exported from abroad, specifically from Serbia and China and the following domestic varietes of Capsicum annum L.: Kolora, Žitava, Dvorská (varieties that form the base of the final product called Paprika Žitava/Žitavská paprika and a mix of a number of domestic varieties called Slovenský polotovar. The tests were conducted in 2015 and 2016. The highest content of pigments in both years was contained in Dvorská and Kolora – 6.81 and 6.11 g.kg⁻¹. The largest amount of total sugars was recorded within Žitava in 2015 (20.5%) and in 2016 Slovenský polotovar with 24.5%. Both the exported as well as domestic products fulfilled the parameters of quality required in the production of sweet pepper.

Effects of processing techniques on drying characteristics, physicochemical properties and functional compounds of green and red chilli (Capsicum annum L.) powder

This study was aimed to investigate the effect of processing techniques on the characteristics of green and red chilli powder. Four samples, such as pretreated green chilli paste (PTGP), pretreated green chilli longitudinal slit (PTGL), pretreated whole red chilli (PTWR) and untreated green chilli paste (UTGP), were prepared and dried at 60 °C in a cabinet dryer. The pretreatment was blanching in acetic acid solution and soaking immediately in a combined solution of Na₂S₂O₅ and CaCl₂. Pretreated samples took a shorter drying time than the untreated sample in reducing moisture content from 86.31 to 8%. Pretreatment before drying resulted in retaining total chlorophyll (~ 86%), phenolic compounds (~ 32%), green color, and pungency of chilli. Analysis result indicated that more than 60% retention of β-carotene was found while retention of ascorbic acid was comparable. Conclusively, this research reveals a good nutritional profile in cabinet dried green chilli powder, which may open the scope for commercial production.

Effects of Blanching and Natural Convection Solar Drying on Quality Characteristics of Red Pepper (Capsicum annuum L.)

The objective of this work was to determine the effects of blanching and two drying methods, open-sun drying and natural convection solar drying, on the quality characteristics of red pepper. A 2 × 3 factorial design with experimental factors as 2 drying methods (open-sun drying and use of solar dryer) and 3 levels of pepper blanching (unblanched, blanched in plain water, and blanched in 2% NaCl) was conducted. Dried pepper samples were analysed for chemical composition, microbial load, and consumer sensory acceptability. Blanching of pepper in 2% NaCl solution followed by drying in a natural convection solar dryer reduced drying time by 15 hours. Similarly, a combination of blanching and drying in the solar dryer improved microbial quality of dried pepper. However, blanching and drying processes resulted in reduction in nutrients such as vitamin C and minerals content of pepper. Blanching followed by drying in natural convection solar dryer had the highest consumer acceptability scores for colour and overall acceptability, while texture and aroma were not significantly (p > 0.05) affected by the different treatments. Therefore, natural convection solar dryer can be used to dry pepper with acceptable microbial and sensory qualities, as an alternative to open-sun drying.