Processing of Capsicums

2015

Standardization, grading and storage of dry chillies

The Bureau of Indian Standards has outlined specified standards for dried chillies based on physical characteristics, as well as on other factors such as total ash, acid insoluble ash, non-volatile ether extract and fibre content. Under the Prevention of Food Adulteration Act (1954), minimum purity standards are laid down for chillies. Agmark specifications for the grading of dry chillies for export takes into account various physical, chemical, sensory and microbiological parameters ().

Microbial and insect infestations are serious problems during the storage of dried Capsicum. Ethylene oxide fumigation in bulk is recognized as the best treatment to achieve practical commercial sterility (). Methyl bromide and phosphene are used as fumigants for insect control. Ionizing radiation with a dosage of 10 kGy has been shown to destroy both microorganisms and insects. A dosage of 7.5 kGy has been shown to be sufficient for eliminating fungal populations, and oleoresin yields have increased from 24.45 % to 31.61% by irradiation due to the enhanced extractibility ().

As mentioned earlier, a large number of products are produced from chilli and paprika. The raw material quality requirements for different end uses vary. In order to satisfy the precise requirements, extensive work has been carried out on chilli breeding. Some of the breeding objectives are given in Table Breeding objectives for major fruit quality traits in various market types of pepper (Capsicum spp.). For the genetic upgrading of oleoresin quality and deeper red colour in Indian chillies, Pusa Jwala was crossed with IC 31339. The new strains attained superiority over parental varieties by possessing 20% and 27.5% more capsaicin and oleoresin, respectively, and a higher colour value (CV) of the order of 22,000 and 27,200 CV, respectively (Wealth of India, 2000).

Table Breeding objectives for major fruit quality traits in various market types of pepper (Capsicum spp.)

Market type Important fruit quality traits
Fresh market (green, red, multi-colour) whole fruits Colour, pungencya, shape, size, lob number, flavour, exocarp thickness, endocarp seed ratio, vitamin A and C
Fresh processing (sauce, paste, canning, freezing) Colour, pungency, flavour, pericarp rhickness, endocarp seed ratio
Dried spices (whole fruits, powder) Colour, pungency, flavour, dry weight, low crude fibre, endocarp seed ratio
Oleoresin extraction Essential oils (colour, pungency)
Ornamental (plants or fruits) Colour, pungency, shape, dry weight

Note: a Qualified for non-pungency or quantified for degree of pungency.

Drying and dehydration

Dried chillies and paprika are the raw materials for the commercially important products of chilli powder, oleoresin and colour. Therefore, the most important primary processing operation for chillies and paprika is drying.

Traditionally, chillies are sun dried to a safe moisture level (about 10%) mainly for transportation, storage, distribution and further processing. Over the years, with the growing demand for speciality products with the required pungency, colour and particle size, along with the information generated on the significance of curing and drying conditions on the functional properties of Capsicum, have lead to the development of improved merhods for their dehydration. The major factor contributing to the product quality is the cultivar. The chemical quality characteristics (oleoresin, colour and ascorbic acid content) of some important varieties of chillies grown in different regions of India are given in Table “Chemical quality of some varieties of chillies”.

In addition to the intrinsic factors, varietal characteristics have also been found to affect the stability of colour in chillies. Lease and Lease () showed that under similar conditions of processing and storage of red peppers as powder for six months, one variety retained 78% of the initial colour while in another, there was almost complete loss. The role of harvesting maturity to colour retention in red chilli powder has been reported (). Subsequent curing of chillies has also been shown to ensure maximum colour formation in paprika (). An important finding on paprika was that there was a more rapid colour deterioration of the low moisture powder stored at high temperature when the harvested fruits were allowed to wither on the plant than when harvested fully mature and ripe and cured outside (). This observation is in accord with the practice of harvest and curing practiced in Hungary and Spain and the continued increase of red pigment concentration during curing outside recorded by many investigators there (). Storing bell pepper after pre-packaging in perforated (0.064-0.42%) polyethylene bags at 3°C gave good colour development which retained the firmness. Under these conditions, the fruits did not develop chilling injury, even at the lower temperature ().

The other important factors are the drying conditions. Sun drying normally takes about 15 to 20 days to reduce the moisture content to 10—15% and under uncontrolled conditions can lead to bleaching and dull colour formation in chillies. Improvements in the sun drying of chillies through pre-treatments, such as pricking, blanching, treating in alkaline solution (dipsol) and drying in preforated trays both in shade and directly in the sun, have been reported by Laul et al. (). By this method, the sun drying time is reduced from 15-21 days to almost a week. Colour and pungency are better retained and a more hygienic quality product is produced. A further improvement on sun drying is the development of the solar drier which effects the complete drying of the commodity in four to five days with much better colour and storage characteristics ().

Mechanical dehydration under controlled conditions of temperature, air velocity and humidity has further improved the quality of dried chillies. Different types of driers, such as the cabinet drier, tunnel drier, multistage belt drier and fluidized bed drier, can be used for the purpose. Controlled rapid drying of plant-withered and sliced fruits at temperatures below 80°C, preferably 60—70 C, has been shown to give the highest colour and colour retention (). In the US, popular chilli varieties are dried in belt driers by a forced draft of air at a temperature of 80°C to a moisture content of 7—8% (). A two stage dehydration, involving initial drying to 12—15% moisture and storage at 0 C and redrying when required for grinding to 7—8% moisture, is also practised. This two stage process has the advantage of better colour and pungency retention. It has been observed that there is a continuation of light induced carotenogenesis in Capsicum after harvest, followed by a light induced degradation of the pigments. By combining a first step of illumination and a second step of darkness during dehydration, it was possible to obtain dry peppers having 20—40% more pigment concentration (). Even under controlled conditions of dehydration certain quality changes take place. Luning et al. () have reported, after hot air drying of Capsicum a decreased levels of odour compounds (Z)-3-hexenal, 2-heptanone (Z)-2-hexenal, (E)2-hexenal and linalool which have green vegetable like, fruity and floral notes. Therefore, it is necessary to optimise the dehydration conditions to minimize the loses.

Dry chillies are usually packed in jute bags of up to 100 kg. In order to prevent breakage of dry chillies while compressing the packs, the moisture content is kept around 10%. Among the various factors affecting dry chillies during storage, darkening due to temperature effect is the most predominant. The present commercial practice is to store dry chillies in cold storages.

Ground chillies

In recent years, the global demand for ground chillies has steeply increased, mainly due to their convenience in use. Ground chillies offer an additional advantage in that it is also possible to get the required functional properties for specific end uses by blending different varieties of chillies. Even though spice grinding is essentially a size reduction unit operation, the requirement of high quality products has prompted considerable engineering improvements. Different types of machines are used for spice grinding. They include attrition mills, impact mills, roller mills, vibro energy mills, fluid energy mills and bowl mills (). Modern spice mills, which handle large volumes, have optimized material flow, closed circuit pneumatic conveying, dust collection aids and noise reduction fixtures (). In order to reduce volatile loss and other quality deterioration due to the heat generated during the grinding operation, cryogenic grinding has also been attempted ().

Hungarian paprika is a specialty product valued for its colour. Fresh paprika is also a rich source of ascorbic acid (vitamin C) which can be as high as 300—400mg/100g. Szent Gyorgi, the Hungarian scientist, was awarded the Nobel Prize in 1937 for isolating ascorbic acid from paprika. Different grades of paprika powder are produced from carefully graded paprika which are not stored for more than one year. The fruits are freed from the calyx and peduncle which dilutes the colour and adds fibre. The placenta, which carries pungency stimulants and seeds which dilute colour and also contribute to the potentially oxidizable fat leading to the risk of colour deteriorations are also removed. The seeds whose addition is required to facilitate grinding are washed in cloth bags to free them from adhering tissues, which may be rich in capsaicinoids. For the pungency grade, the fruits and other parts removed or rejected from other grades are used (). The CFTRI, Mysore, has developed a new technique to fractionate chillies into three grades: (i) Capsaicin rich powder; (ii) Skin; and (iii) Seeds. In the process, the chillies are dried and ground in a suitable mill wherein all three grades are separated. Data from a typical batch show Capsicum rich powder, skin and seeds as 5—6%, 35-40% and 40-44%, respectively (CFTRI Process No. CPS-3560). These fractions can be separately extracted to obtain capsaicin rich oleoresin, colour concentrate and fixed chilli seed oil.

Chilli powder requires suitable packaging to retain its functional properties during storage. These properties are known to be adversely affected by the absorption of moisture, effect of light, oxidation by air and storage temperature.

Capsicum oleoresins

The term “Oleoresin” is used to describe desolventized total extracts by a specified solvent. It sometimes refers to a product obtained by benefication of one or more functional components in the total extracts by some amount of fractionation. In its use as a food additive, the best oleoresin of Capsicum is that which contains the colour and flavour components (pungency, aroma and related sensory factors) and that which truly recreates, when appropriately diluted in food formulations, the sensory qualities of fresh materials (). Being a solvent extracted product, the purity and residual amount of solvent are to conform to the specifications of international and national food laws. Different solvents have been used for extracting oleoresins. The early systematic studies reported by Tandon et al. () have generated the laboratory data for producing chilli oleoresin. They reported the distribution of the functional components like colour and capsaicinoids in chillies. Among the solvents used for oleoresin extraction, they found that alcohol gave the highest yield of oleoresin, but the lowest extraction of colour, while ether gave good yields of both. Mathew et al. () undertook studies to develop a process for producing chilli oleoresins. They found ethylene dichloride to be a better solvent compared to alcohol or hexane. Their studies also showed that 94% of the colour and 90% of the capsaicinoids were obtained by extraction of the chilli pericarp that was freed from seeds and stalks.

The CFTRI has pioneered the developmental work for the establishment of a spice oleoresin industry in India. The process for production of chilli oleoresin developed at CFTRI has been extensively used by the spice processing industry in India. In the process chilli is ground to the required particle size and extracted with a suitable solven.t system. The Regional Research Laboratory, Thiruvananthapuram, India, has also developed a process for the production of chilli oleoresin, including separating fractions of highly pungent oleoresin, colour and seed oil. Counter-current extraction reduces the solvent requirement to 2.5 volumes from 4 volumes for straight runs. During the removal of the solvent from the miscella foaming can be controlled by using anti-foaming agents or air jet control which reduces material loss by entrainment. The last traces of the solvent are removed by steam injection. A vacuum is used in the final stages, as there are very little volatiles in chillies. The spent solvent-free and dried solids contain about 28% protein, 36% carbohydrate and 29% fibre, which could be used in animal feed composition. In the earlier years, ethylene dichloride was a preferred solvent for oleoresin extraction. However, due to their suspected toxicity () poly-halogenated hydrocarbons are discouraged for use in food processing. Presently hexane, acetone and ethyl acetate are the preferred solvents.

There are three types of commercial Capsicum oleoresins (). Oleoresin of Capsicum is mainly used as a food colouring in meats, dairy products, soups, sauces and snacks. Red pepper oleoresin is used for both colour and pungency, mainly in canned meats, sausages, smoked pork, spreads and soups and in a dispersed form in some drinks such as gingerale and in some snacks. Oleoresin from African Capsicum is more pungent and is used for its counter-irritant properties in plasters and some pharmaceutical preparations.

Capsicum colour

In view of the increasing evidence on the carcinogenic potential of synthetic colours, there has been extensive research into the isolation, characterization and use of natural colourants. Capsicum colour (red) is one which has been investigated extensively and produced commercially. Govindarajan () has exhaustively reviewed the chemistry of Capsicum colours, and Francis () has described the use of carotenoids as colourants. More recently, Deli et al. () have made a detailed HPLC analysis of the carotenoids from Capsicum; out of the 56 peaks, 34 have been identified. Capsanthin and capsorubin are the most important colouring pigments in Capsicum. Capsicum colour has assumed great commercial importance as a food colourant. In the past, the application of Capsicum extract was restricted to savoury products due to its spicy flavour. Purified paprika extracts in which the flavour compounds have been significantly reduced, are now available as colours used in sweet preparations such as sugar confectionery. The extract is available in both oil soluble and water miscible forms ().

Due to the commercial importance of natural colours, most of the process information on Capsicum colour is covered under patents. However, some published literature gives useful information. The early report of Todd () gives details of production of Capsicum colour concentrate from fresh red fruits. In the process, red Capsicums are broken mechanically, the pericarp and seed portion are separated and the pericarp is converted into a puree. The puree is passed through a fine sieve to separate juice and pulp. The pulp is reslurried and passed through the sieve to recover maximum colour. The colour components are recovered as a precipitate by the denaturation of the proteins having the sugars, gums and other undesirable components in the solution. The precipitated colour is centrifuged to reduce the water content, drum dried and extracted into acetone. The acetone extract is vacuum distilled to recover the solvent. The resultant ruby-red oil is mixed with permitted antioxidant to prevent colour loss during storage. Preparation of water dispersible Capsicum colour has been described by Elshikiny and Abd-El-Salam ().

Specifications for Capsicum oleoresins

The Essential Oils Association (EOA, 1975) of USA has detailed specifications for three types of Capsicum oleoresins (Table EOA specifications for Capsicum oleoresins). The three types are oleoresin Capsicum, oleoresin red pepper and oleoresin paprika. The pungency standards are determined by diluting an alcoholic solution of the oleoresins in 3—5% sugar solution. This solution is then tasted by panel members and the first perceptible stinging sensation constitutes standard protocols. The strength of the dilution agreed by three of the five panelists gives the Scoville Heat Units (). The Scoville test run shows a very high correlation to total capsaicinoids content (1,50,000 Scoville units =1% capsaicin). The colour value in the EOA specifications is determined by measuring the absorption of a 0.01% solution of the oleoresin in acetone at 458 nm. The absorption is then multiplied by a factor 61,000.

Table EOA specifications for Capsicum oleoresins

Title OleoresinCapsicum (African chillies) Oleoresin red pepper Oleoresin paprika
Number EOA No. 244 EOA No. 245 EOA No. 239
Botanical source C. frutescens L. or C. annuum L. C. annum L. var. longum Sendt. C. annuum L.
Preparation Solvent extraction of dried ripe fruit, with subsequent removal of solvent Solvent extraction of dried ripe fruit, with subsequent removal of solvent Solvent extraction of dried ripe pods and subsequent removal of solvent
Appearance and colour A clear red, light amber or dark red, somewhat viscid liquid with characterisitc odour and very high bite A deep red liquid with characteristic odour and high bite A deep red somewhat viscid liquid with characteristic odour
Scoville Heat Units (for pungency by described method) 480,000 min. 240,000 min.
Colour value (by described method) 4,000 max. 20,000 max. As stated on label (generally 40,000 to 100,000)
Solubility
Alcohol Partly soluble with oily separation Partly soluble with oily separation Partly soluble with oily separation
Benzyl benzoate Soluble Soluble Soluble
Fixed oils Soluble Soluble Soluble
Glycerine Insoluble Insoluble Insoluble
Mineral oils Insoluble Insoluble Very slightly insoluble
Propylene glycol Insoluble Insoluble Insoluble

Geographical appellation and trademarks

Capsicum belongs to that class where certain varieties whose colour, flavour and properties are unique owing to their respective geographic origin. These unique traits may in future become trade mark issues. We need to address this issue very carefully and ensure that proper documentation, both at field and laboratory level, ensures that intellectual crop properties are assigned to the country in question. This issue needs the attention of policy makers, scientists, technologists and others alike.

 

Selections from the book: “Capsicum. The genus Capsicum”. Edited by Amit Krishna De. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2003.