ACTAACTA UNIVERSITATISUNIVERSITATIS CIBINIENSISCIBINIENSIS 10.1515/aucft-2017 -0013 SeriesSeries E:E: FoodFood technology technology DETERMINATION OF THE MORPHOLOGY OF THE STARCH GRANULES AND THE OPTIMUM INTERNAL COOKING TEMPERATURE OF FOUR ANDEAN CROPS: OCA (OXALIS TUBEROSA MOLINA), OLLUCO (ULLUCUS TUBEROSUS LOZ), ISAÑO (TROPAEOLUM TUBEROSUM RUIZ & PAVON) AND ARRACACHA (ARRACACIA XANTHORRHIZA BANCROFT) – Research paper – Omar BELLIDO-VALENCIA*1, Paul K. HUANCA-ZÚÑIGA**, Luis A. MEDINA- MARROQUÍN* * Department of Food Industry Engineering, Universidad Nacional de San Agustín, Arequipa, Peru ** Department of Materials Engineering, Universidad Nacional de San Agustín, Arequipa, Peru Abstract: Andean grains (i.e. quinoa, amaranth) have been increasingly studied in recent times, mainly due to the increase in international consumption. However, Andean tubers other than potatoes have not been so widespread and are mainly studied for their starch, previously extracted. This work studied the morphology of native starch in four of these crops (oca, olluco, isaño and aracacha), during cooking and the evolution of their internal temperature in relation to sensory acceptability. Using scanning electron microscopy, it was determined that the size of crude starch granules was between 9 µm to 38.2 μm for oca, 4.48 to 24.9 μm for olluco, 4.45 to 22.9 μm for isaño, and 5.36 to 23.8 μm for arracacha. Sensorially, it was determined that the optimum cooking temperature for arracacha was 89.1°C, 90.9°C for oca, 91°C for isaño, and 91.4 °C for olluco. All samples had optimal cooking times shorter than potato, with the isaño having the best heat transfer. Keywords: starch; scanning electron microscopy; cooking temperature; starch gelatinisation; andean tubers INTRODUCTION of origin and expressed in different morphology and heterogeneous varieties The Andean crops known today were (Malice, 2009). domesticated by the first inhabitants of South The tubers of oca are cylindrical or ovoid America in the Andean countries, being shaped, averaging 7 to 11 cm in length, those cultivated at high altitude up to 4000 meters of olluco are usually elongated or curved with above sea level. Two of these crops (Zea mays thin skin and little visible buds, while the subsp. mays and Solanum tuberosum L.) were tubers of isaño vary in color and shape (Flores subsequently widely disseminated, now et al., 2003). Arracacha is a tuberous root, the representing a large part of the agricultural edible part of which is a long, cylindrical trade. However, there are edible tubers and cormorous rhizome with horizontal knotted tuberous roots that are underused and used rings (Hodge, 1954), it is also called "Peruvian mainly for consumption by farmers or traded carrot". in small markets, complementing potato Nutritional characteristics (King and Gershoff, cultivation (Bianco and Sachs, 1998; Flores et 1987; Busch et al., 2000) and potential health al., 2003). These include oca (Oxalis tuberosa benefits (Jimenez et al., 2015) of these crops Molina), olluco (Ullucus tuberosus Loz), isaño have been studied, while their processing has (Tropaeolum tuberosum Ruiz & Pavon) and been studied to a lesser extent, although with arracacha (Arracacia xanthorrhiza Bancroft). greater interest in recent years in processed They present a great genetic diversity (Biondi foods such as porridges (Surco Laos, 2004), et al., 2009), which is influenced by the place instant soups, baby food and fried foods 1 Corresponding author. E-Mail address: [email protected] Acta Universitatis Cibiniensis Series E: FOOD TECHNOLOGY 33 Vol. XXI (2017), no. 2 (Santos and Hermann, 1994). However, its al., 2000; Goldner et al., 2012), so there is main form of consumption has remained the little knowledge of the gelatinisation process same, i. e. culinary preparations. of native starch from isaño and arracacha, as Using differential scanning calorimetry (DSC), well as the morphology of their starch granules the starches from these crops have been during the cooking. studied to determine their point of This work aims to determine the most suitable gelatinisation after being extracted from the internal cooking temperature for the sample matrix (Santacruz, 2002; Valcárcel- consumption of these four Andean crops by Yamani et al., 2013, Cruz et al., 2016), and sensory evaluation, as well as to describe the only in the case of oca and olluco the whole morphology of the native starch granules of tubers were studied during cooking (Busch et each product at different cooking times. MATERIALS AND METHODS province of La Unión, in the region of Arequipa, Peru, and selected so that each Samples: The samples of the Andean products sample was made up of specimens of similar oca, olluco, isaño and arracacha were size (Figure 1). acquired in the district of Tomepampa, Figure 1. Samples of Andean tubers Internal temperature evolution:The samples sample was used. All samples were dried to were put in a container containing potable 10% residual humidity, using a moisture water maintained at boiling temperature (92.8 analyser (Chyo Balance Co., Japan), for the °C). Specimens were removed from each time required to maintain a drying temperature sample at certain time periods to measure the of less than 40 °C. internal temperature in the geometric center The sputtering was done using gold at 3 kV using a digital penetration thermometer using the Denton Vacuum Desk II TSC (Hanna Instruments Checkpoint I, USA). (Denton Vacuum, USA) at a vacuum pressure of 50 mmHg. Sixty micrographs were taken Morphology of starch granules:Each sample with the Philips XL20 scanning electron removed from the boiling water was prepared microscope (Philips Co., The Netherlands) for for observation by electron microscopy. Each each sample and then processed with the sample was cut into 3 mm thick slices. For software of the same equipment to get the each Andean crop, an uncooked (raw) control values of size reported as diameter. Bellido-Valencia et al., Determination of the morphology of the starch granules and the optimum 34 internal cooking temperature of four andean crops: oca, olluco, isaño and arracacha Sensory evaluation and optimal cooking time: considered to be better from the consumer In a preliminary experiment, a cooking time point of view. The samples were cooked with range was determined for each product (from boiling water, making measurements in the 26 to 29 minutes for the oca, 28 to 31 minutes geometric center with a thermocouple similar for the olluco, 23 to 26 minutes for the isaño to the procedure of Goldner et al. (2012) but and from 26 to 29 minutes for the arracacha), removing them at the determined times, then within which it was expected to find the drained the water and cooled to room optimal time. The sensory evaluation was temperature before use (Busch et al., 2000). carried out using a panel of 10 members who The results of the sensory evaluation were evaluated the taste, appearance, acceptability treated by an analysis of variance (ANOVA) and aroma, using a scoring test on a structured and the Tukey's test using the version 3.4.1 of scale, comprising milestones from “not very the statistical programming language R (R intense” to “very intense”. High values were Development Core Team, 2008) . RESULTS AND DISCUSSIONS arracacha is a tuberous root and not a tuber like the rest of the samples, as well as the Internal temperature evolution shape and size of the samples that affect heat The isaño and olluco samples had a similar transfer. To the best knowledge of the authors, behavior in their evolution of the internal the internal temperature evolution of these temperature (Figure 2), while the oca and crops has not been previously reported as it arracacha samples had a different and slower was for potatoes (Heinze, 1955) behavior. This may be due to the fact that the Figure 2. Evolution of the internal temperature of the four Andean crops Morphology of starch granules As Table 1 shows, with the start of cooking, The shape of the starch granules in raw oca the average size of the starch granules in all samples was oval, as were the olluco, while samples is increased by swelling of the the isaño and the arracacha were more diverse granules. However, after 4 minutes of cooking in the shape of their granules (Figure 3). The the oca and olluco granules lost their definite isaño starch granules were mainly oval shaped shape, while those of isaño lost their shape but with a small amount of irregular granules after 5 minutes. Up to 5 minutes, the attached to others. In the case of the arracacha, Arracacha granules had maintained their granules with truncated and irregular shapes defined shape and continued to swell to an were observed. average of 18.85 µm. Acta Universitatis Cibiniensis Series E: FOOD TECHNOLOGY 35 Vol. XXI (2017), no. 2 Table 1. Size of starch granules of by raw samples, in µm Sample Raw Cooking for 3 minutes Minimum Average Maximum Minimum Average Maximum size size size size size size Oca 9.00 23.60 38.20 11.80 26.35 40.90 Olluco 4.48 12.43 24.90 5.57 19.14 32.70 Isaño 4.45 13.68 22.90 5.14 14.27 23.40 Arracacha 5.36 14.58 23.80 5.67 15.79 25.90 Figure 3. Micro-photographs of raw starch granules from a) Oca (866x), b) olluco (866x), c) isaño (866x) and d) arracacha (641x) In a study on the morphology of the oca, (2013) reported for oca samples (6.99 to 24.41 olluco and isaño starch granules by scanning µm). electron microscopy (SEM), two different The size and shape of olluco starch granules types of starch grains were revealed: one small were similar to the diameter determined by (less than 7 µm) and not very visible, similar Valcárcel-Yamani et al.