The Effect of Acetobacter xylinum Starter in Waste Liquid Pineapple Peel on the Properties of Nata de Pina

Fresh pineapple waste consisted of saccharides, water, protein, lipid, vitamin and minerals that can be used by beneficiary microorganisms for production another food products. The aim of this study was to investigate physical properties nata de pina made from waste liquid pineapple peel using various starter concentrations and length of fermentation of Acetobacter xylinum. The starter used were 20, 30 and 40% ml. Each 200 mL fresh waste containing the starter was incubated for 14, 21 and 28 days at 29°C. Nata properties such as yield, thickness, fibre and water content were determined. Results showed starter concentration and length of fermentation affect and significantly (P<0.05) different on nata thickness, yield and fiber content. The highest yield (35,75%), thickness (24.6 mm) and fibre content (4.43%) occurred at 40% starter after 28 days of fermentation. However, the optimum nata thickness occurred at 21 days. There is no significantly different (P<0.05) at nata moisture on starter concentration and length of fermentation. In conclusion, waste liquid pineapple peel is potential as a raw material source for making nata de pina with starter Acetobacter xylinum. Keyword: Acetobacter xylinum, Fermentation, Nata de pina, Pineaple peel, Waste Received 2 June, 2020 | Revised 20 July, 2020 | Accepted 20 August, 2020


Introduction
Pineapple (Ananas comosus) is one of tropical fruits that commonly consumed as fresh fruit or processed as preserved food such as canned fruit, jam, syrup, fruit juice and dehydrated products. The main objective of the processing products is to convert fresh pineapple as the perishable fruit into preserved products with longer life. Most pineapples are processed directly after harvest, however, in subsistence farming, the fresh fruits were processed for self consumption or sold to retailers in low price [1]. The waste of the fruit from home industries or large processing industries is produce in large amount of unusable waste material are generated [2]. The by product such as peel, residual pulp consisted of fibre, sugar and nutrients such as vitamins and minerals. Dacera et al., [3] reported the wastes from pineapple canneries have been used as the substrate for bromelian, organic acid, ethanol, etc. since these are potential source of sugars, vitamins and growth factors. Many studies have been carried out and use Acetobacter xylinum through fermentaion in making nata de pina. Nata can be made from any kinds of fruits including pineapple [4,5], the processed product is stable and longer life.
Nata de pina is one of the fermentation culture product of A. xylinum in pineapple juice enriched with carbon and nitrogen under a controlled process. In the nata formation, these bacteria produce enzymes that can convert simple sugar into complex cellulose fibre [6]. The production of nata de pina can be used A. xylinum by inoculating the bacterial starter into pineapple juice [7]. The number of starter and chemical composition of medium used determine nata de pina properties. This studies have focus on the affect starter concentration of A. xylinum and length of fermentation on the yield, thickness, fibre and water content nata de pina produced from pineapple peel as a waste material obtained from fresh pineapple fruit.

Starter Acetobacter xylinum
Inoculum of A. xylinum used was obtained from culture collection of Microbiology Laboratory, Universitas Sumatera Utara. Starter was made by inoculating 20 mL of the bacterial suspension into 500 mL pineapple peel extract. The starter then was incubated for 7 days at 29°C.

Preparation pineapple peel and nata production
A total of 8 kg pineapple peel were obtained from fresh pineapple fruit. The peel was rinsed in running water then sliced (3-5 cm), and homogenated using a waring blender. The homogenate was filtered and 2 L of the filtrate was added with 10 g urea, 200 g sucrose and acetic acid until pH 4. The broth were boiled (100oC), cooled until the temperature 29-30°C. For nata production, the broth (each 200 mL in a sterile 250 ml transparent glass jar) was inoculated to A. xylinum starter with concentrations 20, 30 and 40%. Each of the of the jar was thereafter incubated for 14, 21 and 28 days at 29°C. Each treatment was replicate 3 times.

Determination of thickness and yield of nata
Nata thickness was determined using calipers and the yield (g/v) was determined using gravimetric method with formula as follows:

Fibre content
Nata fibre content was determined according to procedure Badan Stardardisasi Nasional [3] with formula as follows: weight filter paper (g) C = weight filter paper + residue (g)

Nata moisture
Nata moisture was determined according to BSN [4], Five gram of nata in aluminum cup was dried using oven drying for 6 hours at 105oC. The moisture was determined using formula: weight aluminum cup containing nata before dried (g) C = weight aluminum cup containing nata after dried (g)

Statistical Analysis
We employed a completely randomized design factorial. The first and second factors were starter concentration and length of fermentation respectively. We analyzed the observed data using analysis of variance (ANOVA) for statistically significant differences.

Nata thickness
At the first 24 hour in all treatments showed air bubble at the surface of the medium. The fine fibre are distinct after fermentation 48 h particularly at 30 and 40% starter. The white thin layers are become thicker after fermentation 72 h. The higher starter concentration and length of fermenation were followed the increasing thickness as shown in Figure 1. Starter concentrations have effect on nata thickness. Figure 1 shows starter concentration at 20, 30 and 40% after 14    (Table 1).

Conclusion
Acetobacter xylinum as a starter is potential for making nata from waste liquid pineapple peel.
Nata thickness and yield produced the starter more influenced by length of fermentation than that of starter concentrations. Whereas, fibre content was affected by starter concentration and length of fermentation.