Effect of storage time on microbial quality of some spices and dried seasonings

The effect of storage time on the microbial quality of some spices and dried seasonings (SDS) (dawadawa, pepper, ginger, shrimp and fish powders) was studied over a 12-month period. Microbial load and profile of irradiated and unirradiated SDS were assessed at 0, 6 and 12-month periods. The range of total variable counts (TVCs) were initially determined at 0.81-4.53 and 4.65-8.51 log10 cfu g -1 for irradiated and unirradiated SDS, respectively; those for mould and yeast counts (MYCs) were determined at 0-1.74 and 1.55-3.35 log10 cfu g -1 , respectively. Generally, TVCs were not significantly affected (P Bacillus spp., Lactobacillus spp., Clostridium spp., Aspergillus spp. and Penicillium spp ., was stable after the 6 and 12-month periods for all the SDS. However, the profile was consistently more diverse on dawadawa, pepper and ginger powders. No adverse change in microbial quality of irradiated and unirradiated SDS was observed at the end of the storage periods. . L'effet de la duree de stockage sur la qualite microbienne de quelques epices et les assaisonnements seches (EAS) (dawadawa, le poivre, le gimgembre, la crevette et la farine de poisson) etaient etudiees au cours d'une periode de 12-mois. La quantite et le profil microbient de EAS irradie et non-irradie etaient evalues au cours de periodes de 0, 6 et 12-mois. La variation de quantites viables totales (QVT) etait au depart determinee a 0.81-4.53 et a 4.65 - 8.51 log10 cfu g -1 pour EAS irradie et non-irradie respectivement, et celle de quantites de moisissures et de levures (QML) etait determinee respectivement a 0-1.74 et 1.55-3.35 log10 cfu g -1 . En gemeral, QVT n'etaient pas consideblement influencees (P Bacillus spp., Lactobacillus spp., Clostridium spp., Aspergillus spp. et Penicillium spp . etait assez stable apres les periodes de 6 et 12-mois pour tous les EAS. Le profil etait cependant invariablement plus divers sur dawadawa, le poivre et la farine de gimgembre. En general, aucun changement negatif de la qualite microbienne de EAS irradie et non-irradie n'etait observe a la fin de periodes de stockage. Ghana Journal of Agricultural Science Vol. 39 (1) 2006: pp. 93-102


Introduction
Spices and herbs consist of dried leaves, flowers, buds, fruits and bark or rhizome of various plants. Spices and herbs, together with dried seasonings, serve as condiments that contribute immensely to the odour and flavour of foods. Their essential oils also have anti-bacterial properties that have been used in preserving foods. The total world production of spices and herbs in 1997 was 4.5 million tonnes of which 95 per cent was produced in developing countries (Wilkinson & Gould, 1996;Pearson, 1976;Eiss, 2001;CBI, 1999). These products are widely used, especially in the industrial and catering sectors that account for over 60 per cent of the usage in developed countries.
Spices, herbs and dried seasonings are products marketed in the dried state and as such go through long storage or retail periods or both. Wide variations have been observed in product quality, which have been attributed to differences in initial bioburden and processing methods used by local producers. On analysing a total of 120 samples, wide variations of 4.0×10 2 -1.7×10 8 and 0-1.5×10 4 cfu g -1 were reported for total viable cells, and moulds and yeasts of unirradiated products, respectively (Adu-Gyamfi, 2000). Because effective control is lacking over product storage characteristics such as moisture content, packaging, temperature, and humidity in the local SHDS industry, it is essential that the microbial quality be monitored to detect any possible adverse changes. This could help in detecting deterioration in microbial quality during storage and in estimating shelf-life accurately in the local SHDS industry. Production of high quality SHDS would specifically improve catering services and, therefore, boost tourism in the country. It would also help local producers and exporters meet strict hygienic standards and quarantine requirements and, therefore, improve the country's international trade in agricultural commodities.
The objective of this study was to assess the microbial quality of some locally processed spices and dried seasonings and how storage time affects the quality of these products.

Experimental design
Five locally produced spices and dried seasonings (SDS) submitted for contract irradiation by producers at the GTC of GAEC were used in the study. The SDS were the dry powders of pepper, fish, shrimp, ginger and dawadawa. Ten grammes of each SDS were collected before and after irradiation and stored in sterile screwcapped universal bottles under ambient laboratory conditions. For each sample, microbial load and profile were initially determined and further determined after 6 and 12 months.

Irradiation treatment
Twenty grammes of each sample were packed in polythene bags and irradiated at a dose of 25 kGy from a 60 Co source at a dose rate of between 0.112 and 0.128 kGy h -1 at the GTC.

Microbiological analysis
One gramme of each sample was added to 10ml peptone water (1 % peptone water + 0.5 % NaCl) and placed on a mechanical shaker (Junior Orbit Shaker, Lab-Line Instruments, USA) for 15 min. The mixture was then left for about 5 min to allow the coarse material to settle down. Microbial load was determined on the supernatant, using standard decimal dilution and plate count methods (APHA,  (Buchannan & Gibban, 1974), and general fungal flora according to the key of Gilman (Gilman, 1957).

Statistical analysis
Statistical Analysis of Variance with Fisher's pairwise comparison was applied to the data, using the Minitab computer software.

Microbial counts
With the exception of unirradiated ginger powder that had lower counts, the TVCs of all the SDS were not significantly affected (P < 0.05) by the 6 and 12-month storage periods (Table 1). The range of the TVC for the irradiated SDS varied from 0.81-4.53 to 1.01-3.76 log 10 cfu g -1 , and that for the unirradiated SDS from 4.65-8.51 to 4.10-8.36 log 10 cfu g -1 after the 12-month storage period. No coliforms were detected in the samples.
Generally, the MYCs for the irradiated and unirradiated SDS were very low after the 12-month storage period (Table 2). With the exception of dawadawa powder, the counts of the irradiated SDS were not significantly affected (P < 0.05) by the storage periods. Also, with the exception of   Values for unirradiated spices and dried seasonings are in brackets Counts are expressed as log 10 cfu g -1 . Each value is the mean of three replicates Figures in a column bearing the same superscript are not significant at 5 % unirradiated shrimp powder, the MYC for all the unirradiated SDS were significantly reduced (P < 0.05) by the storage periods. Moulds and yeasts were not detected in the powders of dawadawa, fish and unirradiated pepper at the end of the 12month storage period. Fig. 2 shows that pepper and dawadawa powders had a more diverse microbial profile compared to fish, ginger and shrimp powders for unirradiated powders. Aspergillus spp., and Penicillium spp. were the dominant moulds while Bacillus spp., Lactobacillus spp., and Clostridium spp. were the bacteria contaminating SDS (Table 3). Though some differences were observed in the microbial profile of the SDS after the 6 and 12-month storage periods, no pattern could be deduced. Compared to the unirradiated SDS, the irradiated samples had few types of contaminants. No coliforms were detected in the samples.

Discussion
One of the major constraints of the spice and herb industry is difficulty in attaining consistency in product quality due to crude methods of processing. The total number of microorganisms in commercial spices generally range from 10 5 to10 8 cfu g -1 (i.e. 5.0 -8.0 log 10 cfu g -1 ) (Kiss, 1982;Grecz, 1986). Previous work on SDS at the GTC indicated a TVC range of 2.60 to 8.23 log 10 cfu g -1 and that of MYC as 0-4.17 log 10 cfu g -1 for unirradiated samples (Adu-Gyamfi, 2000). These compare well with the range of 4.65 to 8.51 log 10 cfu g -1 (TVC) and 1.55 to 3.35 log 10 cfu g -1 (MYC) recorded in this study. The consistently low levels of moulds have been stressed in other works that have indicated spices to be poor substrates for fungal growth and subsequent mycotoxin production (Madhyastha & Bhat, 1984).
The effectiveness of ionising radiation in reducing microbial load in SDS is well documented (Farkas, 1988;Sharma et al., 1989). Irradiation doses of 10 to 20 kGy reduce TVC to acceptable national and international levels of <10 4 cfu g -1  (i.e. 4.0 log 10 ). This treatment, although almost equal to other commercially established processes including fumigation, is superior because it leaves no residue in the products. This study has further confirmed irradiation as an effective process in reducing the microbial load of SDS to reasonably low levels of 0.81 to 4.53 log 10 cfu g -1 (TVC) and 0 -1.74 log 10 cfu g -1 (MYC). The effect of irradiation is also showed by the relatively less diverse microbial profile of the irradiated SDS compared to the unirradiated SDS ( Fig. 2 and Table 3).
The storage time of up to 12 months did not affect TVC in the SDS, except in ginger powder in which the TVC was reduced at the end of the storage period. The latter observation was also recorded in MYC in unirradiated dawadawa, ginger, fish and pepper powders which had reductions after the storage periods. Because these findings were observed in irradiated and unirradiated samples, they cannot be attributed to the process of irradiation. They could possibly be due to the interplay of factors such as the nature and moisture content of the products, storage temperatures, and humidity or sensitivity of detection methods.
In their natural state, spices and herbs contain many microorganisms that can spoil foods. However, some also contain specific antimicrobial components such as anethol, eugenol and thymol that can reduce potential contamination levels of foods (Aktug & Karapinar, 1986). The predominant bacteria found in spices and herbs are mainly the aerobic sporeformers such as Bacillus cereus, B. polymyxa, B. macerans, B. megaterium, and B. sphaericus as well as Clostridium spp., whilst the fungal microflora mainly consist of Aspergillus spp., Penicillium spp., and Rhizopus spp. (Antai, 1988;Julseth & Deibel, 1974;Schwab et al., 1982).
This study has also confirmed Bacillus spp., Clostridium spp., Lactobacillus spp., Aspergillus spp., and Penicillium spp. as among the dominant microbes contaminating local SDS (Table 3). Coliforms and yeasts are rarely detected in spices and herbs, whilst mould contamination is low (Kneifel & Berger, 1994). This fact has been substantiated by the results indicating absence of coliforms and negligible presence of moulds and yeasts. The absence of coliforms eliminates the threat of potential faecal contamination that could cause serious quality problems. However, unirradiated powders of dawadawa, pepper and ginger consistently had high TVC and relatively more diverse profile throughout the storage periods. The observations necessitate the use of decontamination methods such as irradiation to improve the quality of the SDS.
Although most contaminants persisted in the SDS during the storage period, the microbial profile and counts were not significantly affected after 12 months. This might be attributed to favourable interaction of storage factors such as the nature and age of the product, temperature, humidity and, most importantly, packaging. Effective packaging prevented re-contamination in this study. These findings are of practical value and could assist producers in long-term storage as well as in estimating expiry dates accurately, which is an important shelf-life parameter of SDS in Ghana.

Conclusion
Spices and dried seasonings harbour many bacteria and fungi including potentially harmful organisms. The level of contamination, which is dependent on their origin, processing and chemical nature, is high for dawadawa, ginger and pepper powders. Irradiation is an effective way of decontaminating these products and should, therefore, be integrated into local processing protocols. Although the microbial quality of these products is stable for storage periods up to 1 year, it is necessary to ensure suitable temperatures and humidity as well as effective packaging. Ensuring consistency of quality is vital in sustaining the spice industry, a potential agro-based sector that can boost Ghana's agricultural production and exports.