Effect of Storage (in small Packages) on Volatile Oil and Piperine Content of Ground Black Pepper

: The composition of the essential oil of Sri Lanka black pepper and changes in composition on grinding and storage in various packaging materials are reported.


Introduction
Pepper (Piper nigrum L.) is one of the moreimportant spices grown in Sri Lanka. Sri Lanka pepper is reported to have special characteristics6 (high volatile oil and piperine) which gives it a special position in world trade. Traditionally, pepper has been exported as whole black pepper, however with increasing competition in the world market the need for product diversification has arisen. Among the new forms of pepper for the export market are: ground pepper (black and white), canned and pickled green pepper, buff and white pepper (containing pericarp) and dried green ~e p p e r :~ The original systematic study of the volatile constituents of pepper by Jennings 8,9,11.12.13. 15 and co-workers was carried out using Sri Lanka pepper. However, these studies were directed mainly towards the confirmation of the presence and identification of the constituents of the volatile oil. Although one study '6 gave a quantitative picture of the oil of Sri Lanka pepper, the report is nearly 20 years old. Indian varieties, on the other hand, have been extensively studied and the subject has been given much prominence in a recent review. 6 Thus there is a case for investigating the composition of volatile.constituents of Sri Lanka pepper based on gas-liquid chromatography notwithstanding the fact that the subject was considered in part in a paper on quality control!s 'Past studies 1.2.1.4 on the packaging of ground black pepper have revealed that polyethylene alone does not fully meet the requirements of a ground pepper and in order to retain volatiles, select laminates must be used. Chinenova el aL4 reported reduced losses in lacquered cello~hane, while Balsubrahmanyam elal-" found that low density polyethylene (LDPE) and high density polyethylene (HDPE) were poor barriers for volatile oil while ground pepper in a polyester / polyethylene lined carton lost the least oil. Balsubrahmanyam and Kumar2 reported a 5 month-shelf life using a paper / aluminium foil / polyethylene laminate as well as a cellophane / LDPE double pouch. Balsubrahmanyamet a1 'also reported that high temperature storage in LDPE and H D P E resulted in 'sticky' packages and oil deposition on the surface of the packaging material.
Despite this knowledge, ground pepper continues to be marketed in Sri Lanka in single pouch LDPE.
Our study on packaging of this material appeared important for two reasons:- T o our knowledge the effect of storage in various packaging material on essential oil composition has thus far not been reported.
(ii) It was of interest to determine in more detail the shelf-life of'ground pepper in LDPE as this was the packaging material currently in use in this country.
In this paper we report the following:  (v) The effect of storage (in these packages) on piperine (the pungent principle of pepper).  Chwi ,pad, 5 mm min-1.

Moisture content
Moisture content was determined by the Dean and Stark (toluene) method.5

Oil content
Oil content was determined using Clavenger light oil arm after hydro-distillation for 4h. For the determination of oil content grinding was preceded by freezing. This procedure prevented oil loss.

Oil composition
Oil composition was determined using a Varian 2440 gas chromatograph. Operating and other conditions are given in a footnote of Table 1. Identifications were made using retention data and peak enrichment techniques only. This has been considered adequate as all the components tentatively identified have been previously reported in pepper oil.

Piperine content
Pepper was extracted with CH2CI, and pepper oleoresin produced as described previously? 9' Piperine was estimated by the two methods detailed previously: (i) tlc-uv densitometric method7 and (ii) the tlc-uv spectrophotometric method."

Oil composition of Sri Lanka pepper oil
Oil composition of an export sample'and a sample collected frdm an estate is shown in Table 1. As reported previously"16' monoterpene hydrocarbons were present in relatively large proportions. A significant peak appeared immediately prior to P-caryophyllene (r.r.t = 3.62) conspicuous in Sri Lanka pepper and sometimes occurring in very large proportions. The peak, not reported previously, was unidentified. Beyond r.r.t. = 5.6 were 15-20 minor components whose total contribution was < 8%. No effort was made to identify these components. Table 1 also shows the effect of grinding where the levels of monoterpene hydrocarbons declined to the greatest extent. It appears that some caryophyllene o i a chromatographically similar sesquiterpene was formed during grinding.

Prelimiizary observations
Moisture content was initially 8%. After the various stages of storage, moisture content rose to 9-1496. Mouldiness was not visually observed.

Effect on oil corztent
Oil content declined markedly under all LDPE and the HDPEstorage conditions but remained constant in the aluminium foil laminate and in the tinned can. Some of the results are expressed in Figure 1. (50p m, 100 y m and 175p.m LDPE, 15pm HDPE and A1 foil laminate).

Effect on oil conlposition
Here selected known components were combined under the following categories: (1) nlonoterpene hydrocarbons. (ii) sesquiterpene hydrocarbons and (iii) oxygenates.
In all cases a greater loss of monoterpene hydrocarbons was observed. Sesquiterpene hydrocarbons were also lost, but at a less rapid rate. On a percentage basis the smallest losses appeared to be eqhibited by the oxygenates . Figures 2,3 and 4 describe the rate of loss of volatile oil fractions from LDPE (25p.m) LDPE (175.pm) and HDPE (1 5 p m). Losses of monoterpene hydrocarbons were also shown in the A1 foil laminate and tinned cans after six months of storage; as total oil content did not decline in these cases, the loss of this fraction is probably due to its conversion into other volatiles. Table 2 describes the changes in composition of oil after different treatments and illustrates that the degree of less of constituents is preferential.

Fffcct o)t i)i/~erirre content
Both methods of assay of piperine used in this study gave very closely concordant results.
The only significant decline in piperine content was in the 25pm LDPE ( Figure   5). The figure also shows the loss of volatile oils from the same package. Volatile oil and piperine losses closely parallel one another.  Only identified constituents, present in significant amounts, areshown. Constituents areexpressed as a%of total oil. The piperine levels of the 50 p m LDPE packaged pepper showed a small decline (5%), while no significant decline in piperine content was shown in the case of the other packaging materials.
On washing the .outer surface of 25 p m LDPE with ether, two major components were isolated: (i) piperine-separated by tlc and its identity verified by its uv spectrum and (ii) caryophyllene oxide (tentatively identified by glc and tlc techniques).

Discussion
The composition of Sri Lanka pepper oil does not differ significantly from that reported by the original study of Jennings and Wrolstad.16 However special attention must be drawn to the additional peak at r.r.t = 3.62 which appears to be characteristic of and unique to Sri Lanka pepper oils. This peak has not been identified.
Results show that milling and packaging conditions markedly affect oil content as well as composition. The absence of volatile constituents in the samples from the open market illustrates two facts viz. : (i) little attention is being paid to the method of packaging of ground pepper and (ii) the absence of volatiles does not appear to be an important consideration in local consumer tastes.
However, this will not be true for products destined for the export market. Here, cold or otherwise controlled milling will be required to minimize heat generation and packaging materials will need to be chosen according to the requirements of shelflife. This does not necessarily rule out the use of LDPE as preferential loss of monoterpene hydrocarbons and thereby a n increase in concentration of oxygenates among the volatiles could result in a product more preferred organoleptically.
The study, confirms that both LDPE and HDPE are poor barriers for essential oils and that the thickness of LDPE has a significant effect on not only the rate ofloss of oil but also the composition of the residual volatiles.
The loss of piperine from the 25 micron LDPE is interesting and it is theorised that this compound migrates through the polyethylene facilitated by the movement of oil through the barrier. The detection of caryophyllene oxide on the outer surface of the pouch is not surprising and probably arises by the oxidation of B-caryophyllene; while the less volatile caryophyllene oxide is retained on the outer surface ofthe pouch to some extent, the other hydrocarbons are volatalised.