Post-harvest handling and processing of Capsicums
The genus Capsicum encompasses a number of species differing in size, shape, colour and pungency. Due to these differences some of them are used as vegetables, while most others are valued as condiments and culinary supplements. The post-harvest handling and processing technologies for Capsicum have developed considerably as a consequence of the increased production and newer applications of this crop. Bell peppers and a sizable quantity of chillies are consumed fresh and their harvesting indices and scientific handling protocols have been standardized. Chillies and paprika are initially dried and stored in preparation for processing. The accumulated scientific evidence shows the role of various processing factors on the quality of the processed products like chilli powder, oleoresin and colour extract. In keeping with this knowledge, process parameters have been modified to develop new technologies for obtaining superior products. The emergence of the industrial food processing sector along with newer food applications requiring tailor-made ingredients have also introduced more stringent demands for Capsicum products. R&D and the industry are poised to face the challenges.
Tropical South America is believed to be the original home of Capsicum, where the different varieties were known by different names in regional dialects, one of them being “chilli”. They were introduced into Spain in the fifteenth century by Columbus who named it red pepper. Capsicum is believed to have been introduced into India by the Portugese. The different species of Capsicum which were established in India, China and South Asia are the long and thin varieties of moderate pungency which are locally called “chillies”. The highly pungent varieties having small fruits also called chillies (bird chillies) are more common in Africa. The highly coloured, mildly pungent to sweet varieties known as “paprika” were developed in Europe.
Chillies, red peppers, sweet peppers, cayenne, paprika and most other cultivated varieties of varying pungency belong to the species Capsicum annuum. A few chilli varieties, such as bird chillies (African chillies) and tabasco chillies, are classified under C. frutescens. However, five major cultivated species of the genus Capsicum namely, C. annuum, C. baccatum, C. frutescens, C. chinense and C. pubescens, have been recognized the world over. Regardless of the term Capsicum used by taxonomists, the scientific literature in different countries have used different terms to describe the type of chillies/Capsicums. This practice has lead to considerable ambiguity. The term “chilli” is used in India, the UK, Africa and the countries in the East, but not generally in the US. The British Standard Specifications differentiate between chilli and Capsicum based on the degree of pungency. The International Standard Organization, however, recognizes only two types namely, “chillies” and “paprika”. These types cover the easily perceptible to strongly pungent types and the big fleshy vegetable, and the sweet or just recognizable pungency type of Capsicums, respectively. Commercially, chillies with moderate pungency are grown in tropical countries like India, China, Pakistan, Nigeria, Malaysia, Turkey and Japan; high pungency varieties are grown in Africa and paprika with milder pungency is grown in European countries like Hungary, Spain, Bulgaria, Romania and Poland.
Capsicum annuum is the most important among the species grown all over the world. India is the largest producer of chillies (dry) in the world with an estimated annual production of 1.066 million tonnes during 1996-97 (Annual report, Spices Board 1998-99). Chillies, both fresh and dried, are used as condiments and culinary supplements for their pungency and characteristic pleasant flavour. Bell pepper (C. annuum var. grossum) is used in stews, salads, pizza, meat loaf and also as a vegetable and culinary supplement. Bell pepper is also known by different names, such as green pepper, sweet pepper and in India as Simla mirch.
Over the years, ripe chillies and paprika have become very important raw materials for processing into a variety of products like chilli powder, curry powder, chilli oleoresin and chilli colour. They are also used to a limited extent for canned, frozen, pickled and fermented (e.g. Kochujang) products. Due to their importance in world trade, various developments have taken place in crop improvement, storage conditions, processing technologies as well as the packaging and storage of Capsicums. The large volumes of scientific information generated in the recent years on the beneficial pharmacological properties of capsaicinoids () have further boosted the commercial importance of Capsicums.
This chapter looks into some of the post-harvest technological aspects of this important spice and attempts to shed light onto the future prospects of processing them for value addition.
Handling and storage of fresh produce
Chilli fruits are harvested for use as green vegetables when they are fully mature but before they change colour from green to red. The chilli crop takes about 40 days to flower after transplanting and a further 30 days to develop fruit suitable for green harvest (). Fresh green chillies are usually marketed as such and are only occasionally cold stored. Therefore, very little published information is available on this aspect. The available information as well as the studies carried out at the Central Food Technological Research Institute (CFTRI), Mysore, India, show that the optimum cold storage temperature for chillies is 10 ± 2°C. Under the storage conditions, the storage life of chillies is extended up to 10-12 days. Prepackaging in polymeric film or paper bags improves the storage life and retains the freshness of chillies. It has been reported that the decay in stored fresh chillies caused by Erwinia carotovora is hastened by high relative humidity (). Chillies meant for making dried red chillies are ready for harvest after about 45—50 days of flowering when they are fully mature and red or nearly ripe red.
Some of the important varieties of bell pepper produced in India are: Bullnose, California Wonder, Chinese giant, HC-201, HC-202 and HC-213. They differ in size, shape, flesh thickness and other quality factors. Bell peppers used as a vegetable are usually harvested when they are of market size and still green in colour. Those used for dehydration and sauce are allowed to ripen on the plant before being harvested. Due to their brittle structure, bell peppers should be handled with care. Transpirational losses in bell peppers are very high, limiting their storage life. New Mexican type peppers become flaccid in three to five days () at 20°C (7—10% weight loss). The post-harvest bio-chemical changes associated with the softening phenomenon in C. annuum fruits have been studied (). They showed that the fruit texture decreased with an increase in polygalocturonase activity. Prepackaging of the fruits in perforated polyethylene packages has been shown to reduce water loss rates by 20 times or more (). Prepackaging also reduces colour development (red colour) across nine cultivars on storage (). Based on a Instrumental Sphere data logging tool, potential damage causing operations on the bell pepper packaging line have been identified and remedial measures suggested ().
Bell peppers are susceptible to chilling injury at temperatures below 7°C. Chilling injury also predisposes them to Altemaria rot () and Botrytis rot (). However, pre-harvest spray with growth regulators like paclobutrazol, uniconazole and mefluidide has been shown to alleviate chilling injury development in bell pepper on storage for 28 days at 2°C (). Waxing of the fruits has also been found to be beneficial in extending their storage life (). Other edible coatings (protein, cellulose and oil based) also have been investigated to increase the storage life of green bell peppers. Among them, oil based coating gave the best results in reduction of respiration rate and the preservation of good colour (). As ethylene accelerates senescence in bell pepper, it is not advisable to store them along with other ethylene-producing fruits. Evaporative Cool Storage (ECS) of bell peppers has been shown to extend their storage life to 12 days, compared to two days under ambient conditions. The ECS was maintained at 20-24°C with 95% relative humidity (RH) (CFTRI, 2003).
Pre-cooling of bell peppers before cold storage is essential to obtain good storage life. This is best achieved by forced air cooling. Dipping bell peppers in hot water for four minutes at 53°C and packaging in polyethylene bags was found to be most effective for maintaining bell pepper quality. They remained hydrated and green and had a lower rate of respiration and less chilling injury ().
Low oxygen atmosphere retarded ripening and respiration during transit and storage (). The storage life of bell peppers has been found to be prolonged under controlled atmosphere storage conditions of low oxygen and high carbon dioxide ().
Processing of Capsicums
Future prospects for Capsicums
Being the largest producer of Capsicums in the world, India deserves to have a dominant position in its value addition and export. At present, the country’s export of dry chillies and other products has not reached the desited levels. Therefore, various improvements in the whole chain of ctop production, post-harvest technologies, processing and marketing are required.
Even though undet the Coordinated Vegetable Development Ptogtamme of the Indian Council of Agricultutal Research (ICAR), New Delhi, India, considerable progress has been made in increasing productivity and resistance to diseases, there is scope for further improvements. Today, aflatoxin in dry chillies is a major export issue, which calls for the development of aflatoxin free lines.
Due to vatious reasons, natural plant colourants are acquainting great commercial importance. Among them Capsicum red colour is the most promising, considering its wide application. In India, the promising Capsicum varieties having good colour value and low pungency are Bydagi, Arka Kabir, the Warrangal chilli and KT-Pl-19- They are, however, not comparable to Hungarian paprikas of high colour values and negligible pungency. Therefore, it will be very useful to develop such varieties so that the growing demand for chilli colour can be met better.
The demand for tailor-made chilli products to suit diverse product applications and large scale food processing is increasing. These applications call for the provision of products with the required levels of aroma, pungency and colour, in addition to good storage stability. The accumulated scientific information indicates the importance of the harvesting stage and the primary processing conditions on product quality, especially the colour. This knowledge could be properly utilised to develop new technologies.
It is rather difficult to develop chilli varieties suitable for different product applications. The blending of chilli powders and oleoresins with the help of modern sensory techniques could be standardized to obtain various formulations.
Chilli extracts are presently produced mostly by solvent extraction. Even though the industry is now able to maintain the specified limits of solvent residue levels, there is scope for developing cost effective alternative technologies, such as supercritical gas extraction, which have the additional advantage of selective extraction of components.
Microbial and insect infestations are serious problems in chillies. In addition to the development of pre- and post-harvest protocols, controls in various critical processing steps have to be introduced. In addition to the fumigation and chemical sterilisation practised, irradiation could be further investigated and popularized.
It is needless to state that packaging of the products is critically important for maintaining their storage quality, as well as to aid in marketing. Continuous improvements are possible in this area, along with the development of newer packaging materials having functional properties.
Post-harvest handling and processing of Capsicums: Conclusion
Capsicums, which were used as culinary supplements essentially for their colour, flavour and pungency, have acquired much more importance as a source of natural food colour and valuable pharmacological compounds. In order to maximize the beneficial properties of Capsicum, concerted R&D work is required to develop newer varieties that have higher levels of these compounds. Additionally, technologies have to be continuously upgraded to produce end-product specific Capsicum formulations.
Along with the ever growing nutrition and health conscious consumer, the demand for Capsicums and their products are expected to grow steadily.
Selections from the book: “Capsicum. The genus Capsicum”. Edited by Amit Krishna De. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2003.