Effect of Gamma Irradiation on Microorganisms and Components in Empty Fruit Bunch and Palm Press Fibre of Oil Palm Wastes

Transcription

1 J Sci Food Agric 1990,52, Effect of Gamma Irradiation on Microorganisms and Components in Empty Fruit Bunch and Palm Press Fibre of Oil Palm Wastes Tamikazu Kume, Hitoshi Ito, Isao Ishigaki Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, Takasaki, Gunma , Japan Muhamad LebaiJuri, Zainon Othman, Foziah Aii, Hassan H Mutaat, Mat R Awang and Ahmad S Hashim Nuclear Energy Unit, Prime Minister s Department, Bangi, Kajang, Selangor, Malaysia (Received 6 November 1989; accepted 6 January 1990) ABSTRACT The effects of irradiation on microbiological load and chemical components of empty fruit bunch (EFB) and palm press jibre (PPF) were investigated as the preliminary study for upgrading of oil palm wastes to animal feeds by fermentation. The initial contamination of microorganisms in both EFB and PPF was very high and there is no significant difference between the samples collected from various palm oil mills. The dose required to eliminate below the detectable level was more than 15 kgy for total aerobic bacteria, but 5 4 kgy is enough for fungi. The contents of holocellulose and lignin were c 60 % and 25 %, respectively, in both EFB and PPF, and the change in components by irradiation was small. EFB and PPF have a high water holding capacity suggesting that they are suitable substrates for fermentation. These results show that the irradiation by 5-10 kgy on EFB and PPF is applicable for the pasteurisation of fermentation media without any signijicant change in components. Key words: Gamma irradiation, oil palm wastes, fermentation media, distribution of microorganisms, pasteurisation, holocellulose, lignin. 147 J Sci Food Agric /90/$ Society of Chemical Industry. Printed in Great Britain

2 148 T Kume et a1 INTRODUCTION Empty fruit bunch (EFB) and palm press fibre (PPF) are major cellulosic solid wastes of the palm oil industry. The current availability of EFB and PPF is estimated to be 249 and 2.17 million tonnes (dry weight basis) respectively, which is likely to increase in future (Husin et a1 1985). At present these by-products are mainly discarded or under-utilised. EFB is normally incinerated to produce bunch ash which is used as potash fertiliser or distributed in the field as mulch, while PPF is extensively used as fuel for the production of steam in the mills. However, burning and incineration processes emit a considerable amount of smoke and pollutants, thus affecting surrounding areas. Upgrading of these fibres into useful end products can be expected not only to reduce pollution but also to increase their value. Recently, it has been realised that there is a need to utilise these by-products effectively in order to improve the economic situation of the oil palm industry as well as to reduce pollution problems. Research on the conversion of EFB and PPF into useful end products has been reported. Both EFB and PPF were shown to have considerable potential as animal feeds (Hutagalung and Mahyuddin 1985). Being fibrous, they also provide possibilities for the production of pulp and paper (Kobayashi et al 1985), and with their high carbohydrate content they could be viable substrates for the synthesis of furfural (Ariffin 1985). In spite of these studies, their utilisation is still limited and mainly under experiment. More efforts are required to optimise the utilisation of these oil palm wastes. Gamma irradiation is presently being utilised for sterilisation of medical products and preservation of foods in bulk by virtue of its high penetration ability. Using gamma irradiation we have been investigating the upgrading of oil palm wastes to animal feeds by fermentation. The process is as follows: pasteurisation of fermentation media using oil palm wastes by irradiation, inoculation of useful microorganisms, and subsequent microbial digestion of cellulosic materials as well as production of proteins. This paper describes the distribution of microorganisms in EFB and PPF, and the irradiation effect on microbiological load and chemical components as the preliminary study for the fermentation of oil palm wastes. Materials MATERIALS AND METHODS Samples of PPF and EFB were collected from 15 palm oil mills in peninsular Malaysia (Fig 1). These samples were kept for 2-14 days after the oil extraction process. In addition, fresh samples were also collected from Mill 2. Fresh samples refers to samples collected immediately after discharge from the screw press in the case of PPF and from the stripper in the case of EFB. Gamma irradiation The samples were cut into small pieces (c 2cm long) and used for the assay of microorganisms. For the analysis of components, the samples were ground to a

3 Effects of irradiation on oil palm wastes 149 Fig 1. Locations of palm oil mills where samples collected in peninsular Malaysia. were particle size of 18CL250 pm. These samples (5 g) were packed in polyethylene pouches and irradiated at room temperature using a cobalt-60 slab source at the Japan Atomic Energy Research Institute or the gamma-cell400a at UTN (Nuclear Energy Unit of Malaysia). The dose rates used were 1-10 kgy h-' as determined by Fricke dosimetry. Assay of microorganisms The numbers of microorganisms were determined by the surface plate agar method (Kume et al1983). Total aerobic bacteria and fungi were enumerated separately on Difco nutrient agar and malt-yeast-glucose<hloramphenicol agar plates, respectively. Moisture content The moisture contents of the samples were determined using the Mettler system (Mettler Inst, Greifensee, Switzerland) at 135 C for 4 h. Analysis of chemical components The chemical components were determined in accordance with the modified TAPPI standards method (ANSI 1974). All measurements were done in duplicate and the values were expressed as weight percentage on a moisture-free basis. Water holding capacity The water holding capacities of EFB and PPF were determined (McConnell et al 1974) as follows. Samples (0.45 g), weighed in centrifuge tubes, were stirred in 25 ml distilled water for 16 h. After centrifugation at x g for 1 h the supernate was discarded, the tubes were weighed, and the dry weight of the pellet was measured. Results were expressed as grams of water per gram of dry sample.

4 150 T Kume et a1 RESULTS AND DISCUSSION Distribution of microorganisms in EFB and PPF Samples from 15 mills were enumerated for total aerobic bacteria and fungi. Figure 2 shows the distribution of microorganisms and moisture content in various EFB samples. Total aerobic bacteria ranged from 10' to 10" cells g-', and fungi ranged from lo4 to lo8 cells g-'. All EFB samples collected from various mills were highly contaminated with bacteria and fungi. Contaminations by the microorganisms stood at the same high levels except in the case of the samples from Mill 7 in which the moisture content and the microorganism contamination were relatively low. The results presented in Fig 3 show that total aerobic bacteria in PPF range from lo7 to 10" cells g-' and fungi range from lo4 to lo8 cells g-'. EFB samples have a generally higher moisture content (44-74 %, except Mill 7, 80 - z u 60 c +. C 0 40 " E 20: 3 c u) Mill No Fig 2. Distribution of microorganisms and moisture content in EFB collected from 15 palm oil mills. Unshaded bars, total aerobic bacteria; stippled bars, fungi; cross-hatched bars, moisture content Mil\ No. ~.. 11 I z 60 $ c 0 u 40 $ 3 c 5 20 = Fig 3. Distribution of microorganisms and moisture content in PPF collected from 15 palm oil mills. Unshaded bars, total aerobic bacteria; stippled bars, fungi; cross-hatched bars, moisture content. 15 0

5 Effects of irradiation on oil palm wastes %) compared with PPF (10-38%) because the former is kept outside the mills whereas the latter is stored under shade. The initial contamination by microorganisms in EFB is higher than that in PPF corresponding to the moisture content. However, it is considered that there is no significant difference in the numbers of total aerobic bacteria and fungi between samples collected from the various locations in peninsular Malaysia. Decontamination of microorganisms by irradiation The samples from Mill 2 representing the west coast and from Mill 6 representing the east coast of peninsular Malaysia were selected for the study of radiation inactivation. Figures 4 and 5 show the decrease in numbers of microorganisms in EFB and PPF after irradiation. The inactivation curves of microorganisms in sundried samples are also shown. Bacteria in both EFB and PPF samples were radioresistant, and the dose required for elimination below the detectable level was more than 15 kgy. Fungi were eliminated below a detectable level by irradiation of 5-6 kgy. These results suggest that an irradiation dose of 5 to 10 kgy is sufficient for pasteurisation of EFB and PPF since the decontamination of fungi is important for fermentation using useful fungi, the ph requirement of which is lower than the optimum ph for bacterial growth. Chemical components of EFB and PPF Table 1 shows the chemical components of EFB collected from three mills. Some differences in alcohol/benzene extracts, holocellulose and lignin contents were observed between the samples whereas hot-water solubles and a-cellulose content show no differences. The values obtained were in agreement with those reported by Hush et al (1985). PPF samples from three different mills also showed some variations in their chemical components (Table 2). These variations may be due to L Dose (kgy) Fig 4. Decrease in number of microorganisms contaminating in EFB by irradiation. Symbols: total aerobic bacteria of Mill 2 (0) and Mill I* (A), fungi of Mill 2 (0) and Mill I* (A). *=Sundried sample.

6 152 T Kume et a1 Fig 5. Decrease in number of microorganisms contaminating in PPF by irradiation. Symbols: total aerobic bacteria of Mill 2 (O), Mill 6 (0) and Mill 1* (A); fungi of Mill 2 (O), Mill 6 (m) and Mill 1* (A).*=Sun-dried sample Dose (kgy) TABLE 1 Chemical components of EFB collected from different palm oil mills Chemical component Palm oil mill no Mill 1 Mill 6 Mill I4 Alcohol/benzene extracts Hot-water solubles Holocellulose (a-cellulose ) Lignin Values are means of duplicates and expressed as weight percentage based on moisture-free sample. several factors such as difference in maturity (age) of samples and differences in processing in each mill. Some differences in the chemical components were observed between EFB and PPF. The hot-water-soluble content of EFB was four times higher than that of PPF whereas the level of the alcohol/benzene extract was slightly lower. Cellulose content appeared slightly higher in EFB whereas lignin content was slightly lower. It can be generally concluded that the chemical components of EFB and PPF showed little variation between different mills, and the fermentation conditions are not likely to be affected by such small variation. The results show that both EFB and PPF have a high content of cellulosic components and lignin. It is therefore suggested that it is necessary to use lignin-

7 Effects of irradiation on oil palm wastes 153 TABLE 2 Chemical components of PPF collected from different palm oil mills Chemical component Palm oil mill no Mill 1 Mill 5 Mill 6 Alcohol/benzene extracts Hot-water solubles Holocellulose (a-cellulose ) Lignin Values are means of duplicates and expressed as weight percentage based on moisture-free sample. TABLE 3 Change in chemical components of EFB by irradiation Chemical component Dose (kgy) Unirradiated I Alcoholfienzene extracts Hot water solubles Holocellulose (a-cellulose ) Lignin Values are means of duplicates and expressed as weight percentage based on moisture-free sample. digesting fungi for the fermentation of EFB and PPF. Physical and/or chemical pretreatments for delignification may also be effective in facilitating the fermentation process. Effect of irradiation on chemical components Tables 3 and 4 show the change in components of EFB and PPF by irradiation. Alcohol/benzene extracts and hot-water solubles of EFB were slightly increased by irradiation up to 50 kgy whereas holocellulose and a-cellulose were slightly decreased at a high dose of 50 kgy and lignin content did not change. In the case of PPF, the hot-water solubles were slightly increased but holocellulose and a-cellulose contents seemed to decrease slightly at 50kGy. There is very little effect of irradiation on the amount of alcohol/benzene extract and lignin. From these results it can be concluded that some slight degree of degradation in the chemical components of EFB and PPF has occurred by irradiation up to 50 kgy but the overall effects were not significant.

8 154 T Kurne el a1 TABLE 4 Change in chemical components of PPF by irradiation Chemical component Alcohol/benzene extracts Hot-water solubles Holocellulose (a-cellulose Lignin Dose (kgy) Unirradiated I ) Values are means of duplicates and expressed as weight percentage based on moisture-free sample. TABLE 5 Effect of irradiation on water holding capacities (WHC) Sample WHC (g water g-' dry sample) Unirradiated I0 kgy 25 kgy 50 kgy EFB PPF Sawdust Sawdust (fine) Rice bran Rice bran (fine) Values are means of duplicates. Effect of irradiation on water holding capacity of various samples Water holding capacity is an important factor for the fermentation substrate. Table 5 shows the change in water holding capacity of EFB and PPF by irradiation. The results of the commonly used fermentation media such as sawdust and rice bran samples were also shown for comparison. Both EFB and PPF have a high water holding capacity, and these values were almost the same as those of rice bran and sawdust. These results suggest that they are suitable for use as a fermentation substrate. An irradiation dose up to 50 kgy has no effect on the water holding capacities of all the samples examined. Distribution of microorganisms and components in fresh PPF and EFB samples Table 6 shows the distribution of microorganisms at various stages of postextraction of oil. In fresh EFB sample, the total aerobic bacterial count of lo7 cells g-' increased to lo8 cells g-' in 1-day-old EFB. The sample of EFB (inside) has a lower bacterial count (10' cells g-') and a negligible fungal count. The degree of contamination in PPF increased in the order of hottest, hot and 1-day-old samples. Fungi were below the detectable level in the hottest sample and were detected in the

9 Effects of irradiation on oil palm wastes 155 TABLE 6 Distribution of microorganisms in fresh EFB and PPF Samples Total aerobic bacteria Fungi (cells g-i) (cells g- ) EF B Fresha 1.6 x 107 ND Fresh (inside)b 6.0 x lo2 ND 1 day old 1.1 x x 10 PPF Hottest Hotd 1 day old 1.3 x 103 ND 3.4 x x x x 105 Samples collected on conveyor belt which was immediately ejected from the stripper. Samples collected aseptically from the base of fresh EFB. Samples ejected immediately at the exit of screw press. Samples collected a few hours after exposure to the environment and still within the vicinity of screw press. ND, Below the detection level. TABLE 7 Chemical components of fresh EFB and PPF Chemical EFB PPF component Outer Inner Alcohol/benzene extracts Hot-water solubles Holocellulose (a-cellulose ) Lignin Values are means of duplicates and expressed as weight percentage based on moisture-free sample. hot sample (8 x 10 cells g-, which increased to a level of lo5 cells g- after 1 day of storage). These results indicate that fungi began to infect PPF a few hours after its ejection from the fibre cyclones and increased rapidly during storage under shade. It is apparent from the results that pasteurisation treatment of PPF and EFB is required in order to reduce microorganisms to an acceptable level for fermentation regardless of the stage of the samples except in the case of the hottest PPF. The chemical components in fresh samples were analysed immediately after collection. The results presented in Table 7 show that the chemical components of fresh samples were apparently different from those of the stored samples. The alcohol/benzene solubles were significantly higher in fresh EFB and PPF whereas hot-water solubles were much lower than those in old samples shown in Tables 1

10 156 T Kume et a1 Fig 6. Decrease in number of microorganisms contaminating in fresh EFB and PPF by irradiation. Symbols: total aerobic bacteria of 1- day-old PPF (O), 1-day-old EFB (A) and fresh EFB (0); fungi of 1-day-old PPF (0) Dose (kgy) and 2. Fresh samples were very oily, which accounts for the higher quantity of alcohol/benzene solubles. It is considered that the oil components were consumed in a short time by fungi which grow rapidly on fresh samples. Figure 6 shows the decrease in numbers of total aerobic bacteria offresh EFB and PPF samples by irradiation. Total aerobic bacteria in fresh samples decreased below the detectable level up to 6 kgy irradiation even in 1-day-old PPF which was the most radioresistant. As the initial counts of fungi were low and the fungi was radiosensitive, a dose less than 2 kgy is sufficient to decrease counts below the detectable level. From this result it is clear that minimisation of dose can be achieved by obtaining samples immediately following ejection from the fibre cyclone or stripper so as to reduce exposure to environment and hence to contamination. ACKNOWLEDGEMENTS The authors thank Prof Mohd Ghazali B Abd Rahman and Mr Daud Mohamad of UTN for making possible this cooperative research. We thank Dr S Sato and Dr S Hashimoto for their useful suggestions and discussions. REFERENCES ANSI 1974 American National Standard Technical Association of Pulp and Paper Industry Standard Method T15m-54. American National Standards Institute, Washington, DC. AriMin A A 1985 Furfural from oil palm empty fruit bunches and its potential. Proc Natl Symp Oil Palm By-products for Agro-based Industries. Kuala Lumpur. Husin M, Zakaria Z Z, Hassan A H 1985 Potentials of oil palm by-products as raw materials for agro-based industries. Proc NatE Symp Oil Palm By-products for Agro-based Industries, Kuala Lumpur.

11 Effects of irradiation on oil palm wastes 157 Hutagalung R I, Mahyuddin M D 1985 Oil palm by-products as feeds for animals with special reference to ruminants. Proc Natl Symp Oil Palm By-products for Agro-based Industries, Kuala Lumpur. Kobayashi Y, Kamishina H, Akamatsu I, Hassan A H, Husin M, Hassan K, Mohd Yusoff M N 1985 Thermomechanical pulping and its application to empty fruit bunches of oil palm. Proc Natl Symp Oil Palm By-products for Agro-based Industries, Kuala Lumpur. Kume T, Chosdu R, Ito H, Takehisa M 1983 Effect of gamma-irradiation on fish meal. Agric Biol Chem McConnell A A,.Eastwood M A, Mitchell W D 1974 Physical characteristics of vegetables that could influence bowel function. J Sci Food Agric