Judul: Experimental Investigation on Physical Stability of RPO-in-Water  Emulsion Stabilized by Protein and SiO2 Nanoparticles
Abstrak: As a source of Vitamin-A precursor, the stability of red palm oil (RPO) against oxidation was addressed to be improved. Emulsion containing 10% (v/v) RPO was produced using two-step homogenization, namely at 9000 rpm and 18000 rpm. This research aims to study the effect of emulsification process of RPO to enhance its stability. The used emulsifiers are whey protein concentrate (WPC), soy protein isolate (SPI), and SiO2 nanoparticles with concentration from 2.5% to 15%. The physical stability of the resulting emulsion is analyzed based on the parameters of surface colour, separation index, flow properties, and droplet size distribution. Results showed that higher emulsifier concentration (c) contributes to improve emulsion stability during storage. In this study, emulsion stabilized by SiO2/SPI 15% (SSP15) and SPI 5% (SPI5) were found as the most stable emulsion based on tested physical attributes.
Keyword: emulsion, red palm oil, SiO2 nanoparticle, whey protein concentrate, soy protein isolate

Judul: Sifat Fisik Emulsi Minyak Sawit Merah Distabilisasi
Protein Whey
Abstrak: Whey protein-stabilized oil-in-water (O/W) emulsion presumed feasible to be red palm oil (RPO) “carrier” system. RPO has the potential to be a natural source of pro-vitamin A but its utilization is still limited since RPO tend to have low stability during storage, and its high hydrophobicity nature limits its application on fat/oil-based food. The formation of whey protein-stabilized RPO emulsions (O/W) might overcome those challenges by (i) isolating RPO from the external factors that affect its stability and (ii) “carry” RPO into a non-fat/oil-based food system. For that, a stable whey protein-stabilized RPO emulsion is needed to be a good “carrier” system. This study aimed to (i) develop a stable whey protein-stabilized RPO emulsion with an oil phase content of 30%, (ii) examine and analyze the physical characteristics (visually observed) of emulsions, the characteristics of the emulsion droplets, and both stability during storage, and (iii) evaluate the influence of the droplets characteristics on the physical characteristics of the emulsions and the effect of type and concentration of whey protein used on the physical characteristics of emulsions and its stability. The whey protein-stabilized RPO emulsion was prepared by employing two-steps homogenization with 30% (v/v) oil phase volume fraction. The continuous phase was prepared by making emulsifier solution from two types of whey protein concentrate (WPCa and WPCb) and one type of whey protein isolate (WPI) at four levels of concentration (i.e., 2.5, 5, 10, and 15%; w/v) in deionized water. The emulsions produced were characterized for their droplet characteristics (i.e., average droplet sizes (ADS), droplet sizes distribution, polydispersity index, SPAN, and D-values). The emulsions were then stored at three different temperatures (i.e., 30, 45, and 60 °C), and the droplet characteristics were evaluated after 7 and 14 days of storage. The emulsions stored at 30 °C were also evaluated for their physical (visually observed) stability (i.e., appearance, qualitative rating of destabilization and oil droplet viability, and separation index (SI)). The emulsions with the emulsifier concentration of 15% were further evaluated for their accelerated destabilization rate by the Ostwald ripening and coalescence model. This study was able to form whey protein-stabilized RPO emulsions containing 30% oil phase with good stability. The type and concentration of whey protein used affected the physical characteristics of emulsions, droplet’s characteristics, and the stability of both. The WPCa- and WPCb-stabilized emulsions were more stable, along with lower ADS and SI, than WPI-stabilized emulsions. Besides that, emulsions with higher emulsifier concentrations were more stable, with lower ADS and SI values. The emulsions produced underwent a faster rate of destabilization at higher storage temperatures, and were less stable when stored at above 45 °C. As compared to Ostwald ripening, the coalescence mechanism was thought to be more suitable to explain the destabilization of RPO emulsions tested. Based on its physical appearance, the emulsion with 15% of WPCb was the most stable system, having an SI of 0% after 105 days of storage and initial ADS 398±11 nm. The emulsion also remained stable during extended storage without separation of phase or cream (SI = 0%) up to 220 days of storage. Further
Keyword: coalescence, emulsion destabilization, separation index, whey protein isolate, whey protein concentrate

Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf