1 Introduction. Keywords: Storage, livingstone potato, nutrient components, weight-loss, sprouting, storage

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1 Open Agriculture. 2017; 2: Research Article Open Access Chinelo Vanessa Ezeocha*, Adanma G. Ironkwe Effect of Storage Methods and Period on the Physiological and Nutrient Components of Livingstone Potato (Plectranthus esculentus) in Abia State, Nigeria DOI /opag Received January 31, 2017; accepted March 15, 2017 Abstract: Livingstone potato production in Nigeria is faced with the challenge of high postharvest losses. The aim of this study was to assess the effect of some storage methods on the physiological and nutritional quality of livingstone potato. Potatoes were separated and stored using eight different methods: potatoes stored in3x3x3 ft pits and covered with sand under the shade (T1), potatoes stored in3x3x3 ft pits and covered with ash under the shade (T2), potatoes stored in3x3x3 ft pits and covered with rice husk under the shade (T3), potatoes stored in3x3x3 ft pits and covered with a wood shavings under the shade (T4), potatoes spread on a bamboo platform under the shade(t5), potatoes spread on a raffia palm platform under the shade(t6), potatoes spread on concrete pavement inside the barn (T7), potatoes spread on the ground under the shade(t8), potatoes buried under the ground (T9). T8 was used as the control treatment. Temperature and relative humidity of the environment was monitored, the roots were weighed monthly to access the weight loss, sprouting and rot were observed visually and proximate composition of the stored roots were evaluated using standard methods. The lowest percentage weight loss was observed in samples stored in a pit covered with wood ash and those covered with river sand. Samples stored in pits and covered with wood shavings, wood ash and river sand had the lowest percentage of sprouting (1.63%, 3.45% and 6.06% respectively). The dry matter content increased with storage period in all the storage methods. The starch yield varied in the different storage methods with the samples *Corresponding author: Chinelo Vanessa Ezeocha, Department of Food Science and Technology, Michael Okpara University of Agriculture, Umudike, Nigeria, vanessa.ezeocha@gmail.com Adanma G. Ironkwe, Minor Root Crops Programme, National Root Crops Research Institute, Umudike, PMB 7006, Umuahia, Abia state, Nigeria covered with river sand (13.45%) and the samples buried underground in the field(10.53%) giving the highest starch yield at the end of the storage period. Samples stored under rice husk had the highest ash content (4.77%) while the crude fibre and crude protein contents were highest in the samples spread on raffia palm. The results showed that spreading on the floor or on top of pavements are not good storage methods for living stone potato, however, storage in pits with alternate layers of river sand, wood ash and wood shavings are the best storage methods for livingstone potato. Keywords: Storage, livingstone potato, nutrient components, weight-loss, sprouting, storage 1 Introduction Livingstone potato (Plectranthus esculentus) which is locally known as rizga, is a root crop that belongs to the mint family Lamiaceae. It is indigenous to Africa where it is grown for its edible finger-like tubers (Olojede et al. 2004). This crop contributes significantly to the rural diets and income of many subsistence farmers because it is native, easy to grow and quite nutritious. In spite of these qualities, living stone potato is regarded as neglected and under-utilized specie. The storage of root and tuber crops is a major challenge often beyond the usual farmer s control. It has been reported that reducing postharvest losses would be the next most effective tool for preventing global food shortage (Maalekuu et al. 2014). The primary aim of storage is to prevent deterioration of the quality (physiological and nutritional) of the crop. For storage to be effective, crop losses must be minimised (Takavarasha and Rukovo 1989). Farmers in Nigeria and across Africa store their roots and tubers in various traditional storages such as 2017 Chinelo Vanessa Ezeocha, Adanma G. Ironkwe, published by De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License.

2 214 C. V. Ezeocha, A. G. Ironkwe heap storage, in-ground storage, platform and pit storages (Dandago and Gungula 2011). Kujeke et al. (2015) reported that Livingstone potato farmers prefer to store their seeds in shallow holes dug in the field and covered with straw. These storage methods are relatively cheap for the rural communities since they require minimum materials. There is the need to study the effect of these storage methods on the physiological and nutritional quality of living stone potato. This work was therefore aimed at studying the effects of storage conditions on the physiology and key nutritional components (carbohydrate, crude protein, crude fibre, fat, ash and dry matter content) of livingstone potato to ascertain which storage method may be the best for livingstone potato in Abia state, Nigeria. The results from this work may benefit the farmers, the processors and other researchers. 2 Materials and Methods The experiment was conducted between December, 2014 and March Freshly harvested roots obtained from the Livingstone potato field of the Minor Root Crops Programme of National Root Crops Research Institute, T1: storage in pit covered with river sand Umudike, were randomly sampled. The experimental design was performed using a randomize complete block design (RCBD) and each treatment was replicated three times. The treatments were set up as follows: T 1: Storage in pit (3x3x3 ft) under shade with alternate layers of River sand. T 2: Storage in pit (3x3x3 ft) under shade covered with alternate layers of ash. T 3: Storage in pit (3x3x3 ft) under shade covered with alternate layers of rice husk. T 4: Storage in pit (3x3x3 ft) under shade covered with alternate layers of wood shavings. T 5: Spread on bamboo platform under shade T 6: Spread on Raffia palm platform under shade T 7: Spread on concrete pavement in the barn T 8: Buried underground in the field T 9: Spread on the ground (control) under shade. The temperature and relative humidity of the storage environment were monitored. The weight of the yam tubers were measured at monthly intervals using electronic balance and weight loss expressed as a % of the total weight stored. Sprouting (%) and rot (%) were assessed through visual observation using the method described by Maalekuu et al. (2014). T2: storage in pit covered with ash T4: storage in pit covered with wood shavings T5: spread on bamboo platform T3: storage in pit covered with rice husk T6: spread on raffia palm platform

3 Effect of Storage Methods and Period on the Physiological and Nutrient Components of Livingstone Potato 215 T7: spread on concrete pavement T8: buried underground in the field 2.1 Proximate Analysis Samples were collected at the beginning of the experiment and monthly, proximate analysis was conducted using the AOAC (1990) method to investigate the effect of the storage methods on the dry matter content, crude fibre, crude protein, ash and carbohydrate content. The starch yield was also evaluated using the method of Krochmal and Kilbride (1996) previously described by Sofa-Kantanka and Osei-Minta (1996). 2.2 Statistics Data generated during the study were subjected to Analysis of Variance (ANOVA) using statistics analysis system (SAS Version 9.2, 2009). Means were separated at Least Significant Difference (LSD) of 5 percent. 3 Results and Discussion Table 1 shows the average temperature and relative humidity of the storage areas (under shade, in the barn and in the field) during the period of storage. The temperature under shade was marginally lower than the temperature in the barn while the field had the highest average temperature. The highest relative humidity was recorded in January while the field recorded the highest relative humidity of the three storage areas. The percent weight loss of livingstone potatoes stored with different storage methods for three months were shown in figure 1. Weight loss is an indication of deterioration during storage. This usually occurs as a result of respiration of the stored roots and moisture loss which can be facilitated by high temperatures. This has direct impact on the quality of the stored roots. The peels of livingstone potato roots are relatively thin which makes it easier for moisture loss. The lowest percentage weight loss was observed in T2 (stored in a pit covered with wood ash and T1 (stored in a pit covered with river sand) while the highest weight loss was observed in PS (samples spread on concrete pavement in the barn) with 70% weight loss after 3 months of storage. It was generally observed that samples which were covered lost less weight than the samples which were exposed. The high level of weight loss in the exposed samples may be a consequence of high sprouting and respiration rates caused by direct impact of environmental factors such as temperature and relative humidity. The weight loss could have also been caused by loss of moisture through transpiration which could have been facilitated by high Table 1: Average monthly temperature and relative humidity in the storage areas Months Shade Temp.( o C) Rel.hum(%) Barn Temp. ( o C) Rel.hum(%) Field Temp.( o C) Rel. hum(%) Dec Jan Feb Mar

4 216 C. V. Ezeocha, A. G. Ironkwe Figure 1: Monthly average percentage weight loss of livingstone potato subjected to different storage methods. Where UG = buried underground, RS= stored in a pit covered with river sand, WS = stored in a pit covered with wood shavings, C = control, PS= spread on a pavement in the barn, A = stored in a pit covered with wood ash, RH = stored in a pit covered with rice husk, RS = stored in a pit covered with river sand, B = spread on a bamboo platform, RP = spread on a raffia palm platform. temperature. The percentage weight loss observed in this study was higher than what was reported by Treche and Agbor-Egbe (1996) and Maalekuu et al. (2014) for yams during storage. Sprouting is a major factor that leads to losses during storage. The rate of sprouting increased with length of storage and varied with storage method as shown in Table 2. After one month of storage, sprouting was observed only in the samples stored on concrete pavement (T7), this could be due to free flow of air, conducive temperature and relative humidity. Samples stored in pits and covered with wood shavings (T4), wood ash (T2) and river sand (T1) started sprouting on the 3 rd month of storage and had the lowest percentage of sprouting (1.63%, 3.45% and 6.06% respectively). Mozie (1984) reported that, high rate of ventilation reduces the growth rate of vines in stored tubers, the reverse was observed in this experiment as the samples that were well ventilated (B, RP, C and PS) had Table 2: Percentage Sprouting of Livingstone Potato Stored with different Storage Methods Treatment 1 st month 2 nd month 3 rd month B RP C RH WS RS A PS UG Where UG = buried underground, RS= in a pit covered with river sand, WS = in a pit covered with wood shavings, C = control, PS= spread on a pavement in the barn, A = in a pit covered with wood ash, RH = in a pit covered with rice husk, RS = in a pit covered with river sand, B = spread on a bamboo platform, RP = spread on a raffia palm platform.

5 Effect of Storage Methods and Period on the Physiological and Nutrient Components of Livingstone Potato 217 % Rot Storage methods Figure 2. Percentage rot of livingstone potato in different storage methods. Where UG = buried underground, RS= in a pit covered with river sand, WS = in a pit covered with wood shavings, C = control, PS= spread on a pavement in the barn, A = in a pit covered with wood ash, RH = in a pit covered with rice husk, RS = in a pit covered with river sand, B = spread on a bamboo platform, RP = spread on a raffia palm platform. higher percentage of sprouting than the samples with poor ventilation (T4, T1, T2 and T3). The highest percentage of sprouting (43.14%) was observed in T7 (samples spread on concrete pavement), this could have contributed to the high weight loss observed previously on these samples as sprouting is one of the factors responsible for weight loss (Ravi et al. 1996). The level of rot was generally high in the livingstone potato samples, this could be as a result of the high moisture content which creates an enabling environment for micro-organisms. However samples stored in pits had higher level of decay (as shown in figure 2) which can be attributed to contact with the soil which contains some pathogens. It could also be due to poor ventilation in the pit thereby resulting to build up of heat generated during respiration. A similar observation was made by Maalekuu et al. (2014) during yam storage. The highest percentage rot (52.86%) was recorded on samples stored in pit and covered with rice husk. Figure 3 shows the dry matter content of Livingstone potato subjected to different storage methods at different intervals. Dry matter content ranged from 18.06% (in the freshly harvested samples) to 28.16% in T2 (samples stored in a pit and covered with wood ash after three months of storage). The dry matter content increased with storage period in all the storage methods; this could be attributed to moisture loss during storage through transpiration. A similar observation was made by Treche and Agbor-Egbe (1996) during yam storage. The dry matter content varied with storage methods. The dry matter portion of roots and tubers is mostly composed of carbohydrates which exist primarily in the form of starch and sugars. Starch yield increased after one month of storage in all the storage methods as shown in figure 4. This could be due to the fact that simple sugars in the roots were converted to starch after one month of storage, however, at the end of the three months storage period, the starch yield decreased. The decrease in the starch yield at the end of storage could be because starch was used as a respiratory substrate. The starch yield varied in the different storage methods with the samples covered with river sand (13.45%) and the samples buried underground in the field (10.53%) giving the highest starch yield at the end of the storage period. The ash, fat and crude fibre contents varied significantly (p<0.05) with the storage methods. Table 3 shows the nutritional composition of livingstone potato before, during and after three months of storage. The ash and crude fibre contents increased after three months of storage in all the storage methods. This increase could be apparent due to the high percentage of moisture loss during storage. A similar observation was made by Maalekuu et al. (2014) and Osunde and Orhevba (2009). Samples stored under rice husk had the highest ash content (4.77%) after three months of storage. At the end of the storage period, the

6 218 C. V. Ezeocha, A. G. Ironkwe Storage methods Figure 3: Dry matter content of Livingstone potato subjected to different storage methods at different intervals. Where UG = buried underground, RS= in a pit covered with river sand, WS = in a pit covered with wood shavings, C = control, PS= spread on a pavement in the barn, A = in a pit covered with wood ash, RH = in a pit covered with rice husk, RS = in a pit covered with river sand, B = spread on a bamboo platform, RP = spread on a raffia palm platform. Storage methods Figure 4: Starch yield of livingstone potato subjected to different storage methods at different intervals. Where UG = buried underground, RS= in a pit covered with river sand, WS = in a pit covered with wood shavings, C = control, PS= spread on a pavement in the barn, A = in a pit covered with wood ash, RH = in a pit covered with rice husk, RS = in a pit covered with river sand, B = spread on a bamboo platform, RP = spread on a raffia palm platform. crude fibre and crude protein contents were highest in the samples spread on raffia palm. 4 Conclusions Based on the results from this research, it can be concluded that river sand, wood ash, and wood shavings are the most suitable materials to maintain the physiological and nutritional quality of livingstone potatoes. Spreading on the floor or on top of pavements are not good storage methods for livingstone potato because the roots are not protected from environmental factors resulting in high weight loss, sprouting and significant changes in the nutritional composition.

7 Effect of Storage Methods and Period on the Physiological and Nutrient Components of Livingstone Potato 219 Table 3: Effect of Storage Methods on Nutritional Composition of Livingstone Potato. Sample Moisture Content (%) Ash (%) Fat (%) Crude fibre(%) Crude protein (%) Day a 3.87c 0.68ef 0.75ab 8.21h After one month of storage UG 81.84a 3.30e 2.05c 0.78ab 8.21h WS 81.62ab 3.76c 2.48b 0.66abc 8.27g C 81.11abc 2.69g 0.52g 0.64abc 10.06e PS 80.70bc 3.10f 2.69a 0.61bc 10.51c A 80.36cd 3.48d 0.70ef 0.88a 12.32a RH 80.13cde 4.49a 1.05d 0.34d 10.44d B 79.40def 4.20b 0.74e 0.48cd 8.53f RS 79.12ef 3.30e 0.76e 0.48cd 10.95b RP 78.83f 4.29b 0.66f 0.63abc 10.41d LSD After three months of storage UG 73.10ab 3.51d 0.36d 1.23cd 12.42f WS 74.92a 3.95c 0.40c 1.36b 15.07b C 74.10a 2.84e 0.36d 1.28bc 14.87c PS 72.76ab 3.52d 0.50a 1.03e 13.13e A 71.84ab 3.55d 0.23g 1.25bc 14.47d RH 73.90ab 4.77a 0.33e 1.33bc 13.10e B 73.73ab 4.34b 0.30f 1.13de 13.23e RS 74.26a 3.45d 0.37d 1.04e 15.46a RP 72.05ab 4.45b 0.44b 1.60a 15.32a LSD Means with same superscripts in the same column are not significantly different at 5% level of significance Where UG = buried underground, RS= in a pit covered with river sand, WS = in a pit covered with wood shavings, C = control, PS= spread on a pavement in the barn, A = in a pit covered with wood ash, RH = in a pit covered with rice husk, RS = in a pit covered with river sand, B = spread on a bamboo platform, RP = spread on a raffia palm platform. References AOAC, Official methods of analysis of the Association of Official Analytical Chemists. 15th ed. Washington, DC, Assoc. of Official Analyt. Chemists, 1990 Dandago M.A., Gungula D.T., Effect of various storage methods on the quality and nutritional composition of sweet potato (Ipomea batatas L.) in Yola, Nigeria. International Food Research Journal, 2011, 18, Krochmal A., Kilbride. An inexpensive laboratory method for cassava starch extraction. Uni. Puerto Rico J. Agric., 1966, 50, Kujeke G.T., Masekesa R.T., Kishahayo D., Ngadze E., Mazarura U., A survey of the production practices of Livingstone potato (Plectranthus esculentus) an indigenous and underutilized vegetable in Zimbabwe. Journal of Agriculture and Ecology Research International, 2015, 4(4), Maalekuu B.K., Saajah J.K., Addae A.K., Effect of three storage methods on the quality and shelf life of white yam (Dioscorea rotundata) cultivars Pona and Tela. Journal of Agricultural science, 2014, 6(7), Mozie O., Effect of Air Flow on Weight Losses and Sprouting of White Yam Tubers Stored in the Conventional Barn. Trop. Root Tuber Crops News Lett., 1983, 13, Olojede A.O., Nwokocha C.C., Eke-Okoro O.N., Emehute J.K.U., Varietal response of living stone potato to NPK fertilizer application at Umudike. National Root Crops. Research Institute (NRCRI) Annual Report, 2004, Osunde Z.D., Orhevba B.A. Effect of storage conditions and pre-storage treatment on sprouting and weight loss of stored yam tubers. Journal of Stored Products and Postharvest Research, 2011, 2(2), Ravi V., Aked J., Balagopalan C., Review on tropical tuber crops: II Physiological disorders in freshly stored roots and tubers. Crit. Rev. Food Sci. Nutr., 1996, 36, SAS Version 9.2, Statistical Analysis System. Cary, NC: SAS Institute Inc., 2009 Sofa-Kantanka O., Osei-Minta M., Effect of cultivar and age at harvest on the dry matter, starch gelatinization properties and the cooking quality of cassava. Ghana, J. Agric. Sci., 1996, 29, Treche S., Agbor-Egbe T., Biochemical changes occurring during growth and storage of two yam species. International Journal of Food Sciences and Nutrition, 1996, 47, Takavarasha T., Rukovo A., Food security issues and challenges for the 1990 s. In Rukuni, M Food security policies in the SADC Region. Harare. University of Zimbabwe and Michigan state University Food Security Research in Sothern Africa Project. Department of Agricultural economics and Extension, 1989