treatment on Drying Kinetics of Chilli (Capsicum

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Effect of Carbonic Maceration Pretreatment on Drying Kinetics of Chilli (Capsicum annuum L.) Flesh and Quality of Dried Product Lijun Liu, Yuxin Wang, Dandan Zhao, Kejing An, Shenghua Ding & Zhengfu Wang Food and Bioprocess Technology An International Journal ISSN 1935-5130 Volume 7 Number 9 Food Bioprocess Technol (2014) 7:2516-2527 DOI 10.1007/s11947-014-1253-6

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Author's personal copy Food Bioprocess Technol (2014) 7:2516–2527 DOI 10.1007/s11947-014-1253-6

ORIGINAL PAPER

Effect of Carbonic Maceration Pre-treatment on Drying Kinetics of Chilli (Capsicum annuum L.) Flesh and Quality of Dried Product Lijun Liu & Yuxin Wang & Dandan Zhao & Kejing An & Shenghua Ding & Zhengfu Wang

Received: 12 August 2013 / Accepted: 6 January 2014 / Published online: 25 January 2014 # Springer Science+Business Media New York 2014

Abstract A new pre-treatment — carbonic maceration (CM) pre-treatment — was presented in this paper. To study the effect of CM on microwave drying (MD) kinetics of Chilli flesh and quality of dried product, the fresh (control group, CK) and CM pre-treated samples were dried through MD at 100, 150 and 200 W, respectively. CM conditions were optimized by orthogonal test. The drying results indicated that, the average drying rate for CM samples were as much as 150– 185 % of these for CK samples. For both CK and CM samples, the drying rate increased at the initial time (a warming-up period) and then decreased at the end time (a falling rate period) after reaching a plateau (a constant rate period). And the effective diffusivity, Deff, increased gradually at the initial period and then rapidly at the final period with the diminishing moisture content. Elevated microwave power levels could lead to a linear increase in values of Deff at the same moisture content. The activation energy, Ea, increased rapidly when moisture content was below about 1 g water/g dry mass, which was lower for CM samples than for CK samples, and can be well described with a logistic model. Scavenging free radical capability (DPPH), ferric reducing antioxidant power (FRAP), total phenol contents and vitamin C retention contents of the dried products for CM samples were as much as 170.1–190.9 %, 140.2–147.8 %, 140.1– 160.0 % and 212.7–682.4 % of these for CK samples, respectively. The CM dried products were also better in terms of colour differences than CK. L. Liu : Y. Wang : D. Zhao : K. An : S. Ding : Z. Wang (*) College of Food Science and Nutritional Engineering, National Engineering and Technology Research Centre for Fruits and Vegetable Processing, Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, China Agricultural University, POB 303 of China Agricultural University, Qinghua East Road Number 17, Haidian District, Beijing, 100083, China e-mail: [email protected]

Keywords Chilli flesh . Carbonic maceration . Microwave drying . Effective diffusivity . Activation energy . Antioxidant capability

Introduction Chilli (Capsicum annuum L.) peppers are one of the most popular spices in China and other parts of the world. Chilli also has the highest vitamin C (VC) content among vegetables and contains high amounts of vitamin A, beta-carotene, and minerals. In the food industry, capsicums (resource of Capsaicinoids) are used as colouring and flavouring agents in sauces, soups, processed meats, snacks, candies, soft drinks and alcoholic beverages (Pino et al. 2007). Capsicums also can be used in pharmaceutical industry. To date, research has shown that capsaicinoids, and capsaicin in particular, have a wide variety of biological and physiological activities which provide them functions such as anti-oxidation (Materska and Perucka 2005), anticancer (Macho et al. 2003), antiinflammation (Sancho et al. 2002), promotion of energy metabolism and suppression of fat accumulation (Ohnuki et al. 2001). Chilli is generally dried through solar drying and has a low moisture content (MC) of 8–10 % w/w (db) for storage; it ranks second among primary vegetable crops after Chinese cabbage in China (Xu et al. 2008). However, the conventional solar drying not only is time-consuming and high in energy consumption but also produces products with poor quality and severe contamination. In addition, hot-air drying is also timeconsuming. Recently, applications of microwave drying (MD) were increased abundantly because of its advantages such as higher drying rate and shorter drying time as compared to the conventional hot-air drying, decreasing energy consumption of the dried products (Ding et al. 2012). Microwave heating

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involves the interaction of microwaves with a nonhomogeneous food product, which contains materials highly affected by the electrical component of the electromagnetic field. Water is the most common polar molecule and is a major component in most foods, thus water primarily acts as the polar molecules to produce heat. When microwave energy is used for heating food, heat is primarily generated within the food, the heat flow enhances the mass flow because of the same direction, both from inner to outside of the samples, and thus the time for the food to reach final MC is reduced. Air in the oven and the food container is warmed only when they receive heat from the food. Thus, microwaves provide an energy efficient process. The increased pore size, due to puffing effect of microwave, provides easy diffusion of moisture through the sample resulting in a high mass transfer rate (Mudgett 1989). Before drying, different treatments are often used not only to increase the drying rates but also to preserve the nutritional and organoleptic quality of the dried products (Femenia et al. 1998). Chemical pre-treatment (e.g., immersing products in solutions of chemicals, such as sodium and potassium hydroxide, potassium meta bisulphate, potassium carbonate, methyl and ethyl ester emulsions, ascorbic and citric acids) can increase the drying rate by removing the surface resistance of mass transfer in fruits and vegetables (Doymaz 2009). Osmotic pre-treatment (Chenlo 2006), thermal blanching (Sonia et al. 2011) and high pressure treatments (Sonia et al. 2008) on peppers have shown the benefit for shortening the drying period. However, chemical pre-treatment may cause food safety problems; the problem with chemical waste disposal is also an issue. Thermal blanching and osmotic pretreatment likewise present a problem of wastewater disposal. As for high-pressure treatments, the equipment cost is still too high for the moment. To develop a pre-treatment which can avoid these problems, we applied a brand new technique, named carbonic maceration (CM) technique, before MD of the chilli. Invented by Michel Flanzy in 1934, CM involves placing the intact grape clusters into a closed tank with a carbon dioxide-rich atmosphere. CM technique has been used in cabernet making, grape juice making and sugar production (Berovic et al. 2003; Gunes et al. 2005; Alnia et al. 2010). CM process can effectively induce some physicochemical reactions in plant tissues, such as hydrolysis of high polymer and anaerobic fermentation. The detailed information has been included in Table 1. The CM results involve a cytoplasm pH decrease, explosive cell rupture, modification of a cell’s membrane, inactivation of key enzymes and extraction of intracellular substances (Gunes et al. 2005). A reduction in degree of polymerization as well as in degree of methyl and acetate esterification in chilli releases some bound water into free water and enhances the moisture permeability in the plant tissue; free water has higher dielectric properties than bound

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water, so the efficiency of MD is increased. The synergy effect with MD mode gives higher drying rate and better product quality. Grapes have high sugar content and CM can lead to a complete fermentation. But peppers have low sugar content and people may have doubts about the fermentation effect. To determine the CM fermentation effect on drying kinetics of peppers and quality of dried products, we adjusted the method to lead to an incomplete fermentation, i.e., to keep CM fermentation of peppers not leading to a plant tissue collapse in terms of organoleptic quality of the products. Therefore, chilli samples pre-treated with or without CM were dried by MD. And then the MD kinetics curves of chilli regarding moisture ratio (MR), drying rate (DR), moisture effective diffusivity (Deff), activation energy (Ea), and the quality indices of dried products such as ferric reducing antioxidant power (FRAP), scavenging free radical capability (DPPH), total phenol contents (TPC), ascorbic acid retention rate (VC RR, %) and colour were determined to evaluate the effect of CM pretreatment on drying kinetics of peppers and quality of dried products.

Materials and Methods Plant Material Fresh chilli were bought from a local market and selected by noticing that all the samples could be free-disease, almost uniform in shape (length 9.0±0.5 cm) and colour. They were stored at 4°C and relative humidity (RH) of >95 % until used in the experiment. The peppers were sliced, and their seeds were removed before the pre-treatment or drying. Orthogonal Test Effect of independent variables such as CM pressure (A), duration (B) and temperature (C) on responses such as drying time (DT), colour difference (ΔΕ*) and VC retention rate (VC RR, %) was investigated by an orthogonal L9(3)4 test design (Table 2). According to the orthogonal test results, optimization of the CM pre-treatment conditions was carried out by the extreme difference (R) analysis. Carbonic Maceration Pre-treatment CM equipment was designed by the corresponding author (Fig. 1). Triplicate samples of peppers were weighed and placed in CM tanks. The tank was filled with CO2 to a desired pressure via two adjusting valves and then put into a thermostatic bath, with which the CM temperature can be regulated. According to the results of the orthogonal test, the CM pressure, duration and temperature were set at 0.2 MPa, 30 h and

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Table 1 Reactions took place during carbonic maceration (CM)

Locations

Reactions Pectin

Cellulose

Beta galacturonic acid

Glucose

Cell wall Hemicelluloses

Arabinose

(Krall & McFeeters, 1998)

Membrane

Membrane lipid

Fatty acids

Vacuole Liu & Wang, 2011

Xia & Gao, 2009

Liu & Wang, 2011

Results

Cell wall collapsed; Capillary ruptured; High polymer became low polymer; Cell wall permeability increased; Bound water decreased

Membrane permeability increased

Vacuole ruptured; Cell wall collapsed; Capillary ruptured; pH decreased; Phenols increased; Bound water transformed into free water

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Table 2 Experimental design and results: effect of carbonic maceration (CM) pre-treatment on drying time (DT, min), vitamin C retention rate (VC RR, %) and ΔE * Index

DT (min)

VC RR (%)

ΔE*

Run

A

B

C

DT (min)

VC RR (%)

ΔE*

1 2 3 4

1 (0.12) 1 (0.12) 1 (0.12) 2 (0.16)

1 (18) 2 (24) 3 (30) 1 (18)

1 (30) 2 (35) 3 (40) 2 (35)

110±10c 103±3c 83±6b 107±12c

29.4±0.4b 29.2±1.6b 50.6±0.5d 46.1±1.1c

16.5±0.2d 18.8±0.2b 19.4±0.2e 18.5±0.1cd

5 6 7 8 9 K1 K2 K3 R K1 K2 K3

2 (0.16) 2 (0.16) 3 (0.20) 3 (0.20) 3 (0.20) 296 343 289 18 109.2 154.9 165.2

2 (24) 3 (30) 1 (18) 2 (24) 3 (30) 300 399 229 57 131.2 107.5 190.6

3 (40) 1 (30) 3 (40) 1 (30) 2 (35) 296 293 339 15 162.5 133.5 133.3

173±6e 63±6a 83±6b 123±6d 83±6b B>A>C

27.0±1.5a 81.8±1.5g 55.7±0.5e 51.3±1.8d 58.2±1.1f

24.5±0.2g 14.6±0.2a 18.4±0.1cd 20.0±0.1f 19.4±0.1e

R K1 K2 K3 R

18.7 54.7 57.6 57.8 1.0

27.7 53.4 63.3 62.3 3.3

9.7 51.1 56.7 62.3 3.7

B>A>C

C>B>A

A, B and C are the variables respectively representing CM pressure (MPa), duration (h) and temperature (°C); coded numbers 1, 2 and 3 in columns A, B and C are the coded levels of the variables, and the numeric values in parentheses are the uncoded levels. Ki (i=1, 2 and 3) is the sum of response to the variable at ith level. R is the range difference between the maximum and minimum of Ki in the same column. Different letters in the top right corner of numeric values indicate a significant difference (p