effects of electron-beam irradiation on physicochemical ... - OpenAgrar

ISSN: 1579-4377

EFFECTS OF ELECTRON-BEAM IRRADIATION ON PHYSICOCHEMICAL PROPERTIES OF OIL PALM FROND BASKETS Paul Chidozie Onyenekwe*1, Mario Stahl, Ralf Greiner Max Rubner Institut, Bundesforschungsinstitut für Ernährung und Lebensmittel, Molekularbiologisches Zentrum, 76131 Karlsruhe, Germany. [email protected].

ABSTRACT Palm frond baskets have been an integral part of packaging in many countries and have formed part of the local culture such that certain agro products are assumed to be in their best when packaged in palm frond baskets, hence many resist the use of synthetic materials. Irradiation of materials requires pre-packaging; there is the need therefore to understand the effect of irradiation on the biomaterial and determine the possible parameters that can be used for identification of irradiated materials. The effect of electron beam radiation treatment on the physicochemical properties of oil palm frond basket was investigated. Irradiated baskets showed a dose dependent ESR signal intensity and retained more than 13 % of the signal 30 days post-irradiation. Irradiation had no effect on the hygroscopicity. Headspace analysis showed no significant difference in the composition of the constituents, however differences in per cent content of 2-methyl-1-penten-3one, 3-methyl-butanal, decanal, heptanes, 5-hepten-2one and dodecamethyl cyclohexasiloxane were observed. Palm frond baskets can be used as packaging material for agricultural produce meant for irradiation and ESR could be used to differentiate irradiated and non-irradiated baskets. Heptane and 2-Methyl-1-penten-3-one which increased by over 500 times post-irradiation can be candidates for identification of irradiated baskets. KEYWORDS Cellulose, ESR, hygroscopicity, headspace, packaging, radiation.

Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]

INTRODUCTION Oil palm (Elaeis guineensis. Jacq) is one of the major cash crops of Nigeria and was the major foreign exchange earner of the defunct Eastern Nigeria before the discovery of petroleum. It also grows well in other wet and humid places like Malaysia (Basiron, 2007) which is now the world highest producer of palm oil (Chew and Bhatia, 2008). Apart from palm oil and palm kernel oil which are the main articles of trade from oil palm, other parts such as the trunks, fronds and kernel shells are used in house building and decorations. The empty fruit bunch is used in soap making, mushroom production and the fronds used in basket making and fences. With the advent of modern building materials, basket making has become the main use of the fronds. The major use of these baskets is the transport of agricultural produce like tomatoes and other horticultural fruits (Adegoroye and Eniayeju, 1988) and sundry uses like in palm oil production (Taiwo et al, 2000). These fruits are usually harvested at the climacteric stages while still strong and transported in baskets. In most developing countries, major losses occur in the post-harvest distribution of horticultural produce (Holt and Schoorl, 1981). Most losses result from damage caused by static and dynamic stresses during transit (Olorunda, and Tung, 1985), and by rough handling during loading and unloading (Dahlenburg, 1983). Although some impact-induced damage is caused by shocks during transportation, but dropping during container stacking and destacking is more important (O'Brien, et al. 1965). Comparing cane and oil palm frond baskets Adegoroye and Enaiyeju (1988), observed that fruits packed in cane baskets were more susceptible to impact-induced damage of all defect categories than oil palm fronds. They observed that the total damage was three times greater in cane than in frond baskets and no visible impact damage was noticed on any of the baskets. Hence fronds have advantages over cane basket as high tensile and compressive strength materials. Oil palm frond has been found to be composed of ash 0.70 – 2.4%; lignin 15.2 – 20.5%; holocellulose 82.2 – 83.5%; (Wanrosli, et al. 2005, Abdul Khalil et al. 2006); cellulose 39.0 – 52.7%; (Wanrosli, et al. 2005, 2007; Sun et al. 2005; Xu et al 2005) depending on the method of determination and hemicellulose 33% (Fazilah et al. 2009). Most packaging materials are made of natural or synthetic materials and are often subjected to ionising radiation when used in packaging of goods that are to be irradiated. The effect of radiation on these materials is very crucial for the choice of packaging material based on the intended dose. Palm frond consists of mainly holocellulose and lignin (Abdul Khalil et al. 2006; Wanrosli, et al. 2007). Although lignin constitutes a small fraction of the frond, since baskets is made from the frond bark (Soyebo et al. 2005), which is highly lignified, lignin therefore may constitute a high fraction of the material. The functional significance of lignin has been associated with the mechanical support (Boudet, 2000). Lignin has been implicated to play a role in photodegradation of wood (Feist, and Hon, 1984). Yellowing of lignocellulosic materials and woods surfaces indicates the modification of lignin and holocellulose. Cellulose undergoes chain scission when irradiated resulting in a loss in mechanical properties. The government of Nigeria through its agency, Nigeria Atomic Energy Commission (NAEC), has recently established an irradiation facility at Abuja. More than one year after the commissioning of this facility it has been very difficulty getting farmers convinced to spent extra money to acquire plastic crates and jettison their traditional packaging material. The aim of the project was to determine the effect of irradiation on the physicochemical

1007


properties of oil palm frond basket and propose parameters that can be used to differentiate irradiated and non irradiated baskets using physicochemicals parameters. MATERIALS AND METHODS MATERIALS Fresh oil palm frond materials were prepared into stripes in making small baskets. These were allowed to equilibrate with the ambient conditions for two weeks before they were subjected irradiation. METHODS IRRADIATION The samples were irradiated at ambient conditions at a dose level of 0, 5 and 15 kGy using a linear accelerator (10 MeV, 10 KW). The dose rate was approximately 107 Gy/s. Irradiation was carried out in the presence of air at room temperature at the plant of the Beta-GammaServices GmbH & Co KG (Bruchsal, Germany). The dosimetry was carried out by Alanin dosimeters, the detection methods used were Photostimulated Luminescence Method (PSL) and Electron Spin Resonance Method (ESR). Irradiated samples were re-irradiated three weeks and the effect determined. PHYSICOCHEMICAL ASSESSMENTS WATER SORPTION ISOTHERM Water sorption isotherms were determined by the gravimetric method. Samples were stored in humidity chamber (Tritec®, Hannover Germany). The experiment was carried out at 35oC. Moisture content was calculated on initial-dry weight basis using the equation: M = (W - Wi/Wi) x 100%

⎛ W − W i ⎞ M = ⎜ ⎟ x100% ⎝ W i ⎠ where W and Wi were the weight (g) of the baskets at measured conditions and initial dry weights respectively. € ESR SPECTROSCOPY ESR measurements were carried out according to European Standard for the detection of cellulose radicals using EN 1787 (2001). Palm frond strips fine strips and transferred to 4.0 mm quartz capillary tubes and packed with gentle tapping to a length of 30.0 mm (active length) in triplicates, and the weight of the sample was determined. The results for the signal intensity of samples were normalized to the packing weight. ESR measurements were

1008


performed using a Bruker Biospin spectrometer (E-Scan, Bruker, Germany). All of the spectra were recorded at ambient temperature of the ESR laboratory (27°C). Operating conditions of the ESR spectrometer were as follows: centre field, 3488 G; sweep width, 180 G; microwave power, 1.653 mW; microwave frequency, 9.808 GHz; modulation frequency, 86.00 kHz; Mod. Amplitude: 4.60 G; receiver gain, 3.17e+002; sweep time of 5.243 s and time constant, 40.960 ms. PSL MEASUREMENTS The photostimulated luminescence (PSL) measurements were carried out as described by EN 13751 (2002), using a SURRC PPSL Irradiated Food Screening System (SURRC, Glasgow, United Kingdom). The PSL system (serial; 0021, SURRC; U. K) was used for PSL measurement of the whole samples (c5 g) placed in a disposable Petri dish with a 50 mm diameter (Bibby sterlin type 122, Glasgow, U. K). The PSL signal was recorded at a rate of counts/60 s for both the control and the irradiated samples. The emitted PSL signals (photon counts, PCs) from the sample per second were automatically integrated in the PC and presented as counts/60 s. Two PSL signal thresholds, the lower threshold (T1, 700 counts/60 s) and upper threshold (T2, 5000 counts/60 s) were compared. Under this, three classes of samples are possible namely, positive, intermediate and negative. The intermediate which is in between the two thresholds requires further investigations to ascertain whether the test samples have been irradiated or not. Post-irradiation storage and handling of the samples were carried out in the dark and under yellow light respectively. EXTRACTION–GC/MS ANALYSIS The extraction procedure of the samples was carried out as follows: Samples of 1.0 g each from both control (non-irradiated) and irradiated fronds were cut into small pieces approximately 0.05 - 0.5 cm. A Schimadzu GCMS-QP2010 Plus was utilized to obtain chromatograms of the extract. The separation was performed on a HP-5MS fused silica column (5% phenyl methyl polysiloxane 30m×0.25mm i.d., film thickness 0.25 µm). The oven was held at 50O C for 2 min during injection then temperature programmed at 5 °C min−1 to a final temperature of 210 OC and held for 5 min. Injection temperature was kept at 220 OC all the time. Fivemicroliter volume of essential oil was injected into the GC. Helium carrier gas at a constant flow-rate of 0.68 mLmin−1 and a 5:1 split ratio were used simultaneously. Mass spectrometer was operated in full scan and standard electronic impact (EI) modes with electron energy of 70 eV. Interface temperature: 280OC; Ion source temperature: 200OC; MS quadruples temperature: 160OC. In the range of m/z 45–350, mass spectra were recorded with 3.12 s scan−1 velocity. RESULTS AND DISCUSSION The water sorption isotherms at 35 °C of the samples, non-, single dose, and double dose irradiated samples are shown in figure 1. The isotherms are of the sigmoidal form, which is type II isotherm. The hygroscopicity of the baskets was not affected by irradiation or reirradiation. Although Liu et al. (2005) had observed increased water absorption in microwave irradiated cellulosic materials due to rapture of the radial parenchyma and some

1009


pit membrane which then serve as artificial channels of liquid and gas; our result may be an indicative of non-disruption of these tissue components of the plant material. This may explain the observation of Despot et al, (2007), who observed that gamma irradiation of wood, a cellulosic material, up to 150kGy had no significant effect on the maximum swelling and total water soluble carbohydrates. Depolarisation of cellulosic materials had been shown to be more when irradiated in pulp than in wood form (Skvortsov and .Klimentov, 1986).

Moisture Content (g/100g)

18 16 14

0kGy

12

1kGy

10 8

1kGy R

6

5kGy

4

5kGy R

2

15kGy

0 70%

15kGy R 75%

80%

85%

90%

95%

100%

Relative Humidity (%)

Figure 1: Water sorption isotherm at 35oC of the baskets of different doses (R stands for re-irradiated or double irradiation 22 days after the first irradiation.

ESR SPECTROSCOPY Non-irradiated palm frond strip exhibited one weak singlet ESR line characterised by g = 2.011±0.0095 centred around 3486 G without any satellite peak (figure 2a). This ESR spectrum is known to be typical of non-irradiated plant materials. Although the origin of the free radicals responsible for this spectrum is not well understood, it had been opined to be semiquinones-like radicals produced by the oxidation of plant polyphenols (Swartz et al 1972) or lignin (Maloney et al 1992; Tabner and Tabner, 1994). Lignin had been shown (Abdul Khalil et al. 2006, Wanrosli et al.2007) to constitute 15.2 – 20.5% of palm frond and this may explain the observed ESR signal of the non-irradiated samples. Irradiation of the palm frond produced more enhanced spectra of the same singlet ESR line with two symmetric satellite peaks (figure 2 b, c and d) on the left and right of the main peak with a distance of 60.0G in between them. Hence the frond exhibits cellulose-like ESR spectrum. The relationship between dose and ESR signal amplitude (satelite peaks) is shown in figure 3. There was no correlation between dose given and the signal amplitude after the first treatment. The amplitude of the 15 kGy treated sample was 9.5x and 8.1x that of 1 and 5 kGy samples respectively. However re-irradiation of the samples twenty-two days later gave a linear regression with y = 99957x + 61086 and R2 = 1. Re-irradiation although

1010


significantly (p