Nowadays, probiotics offer a promising alternative approach for controlling shrimp diseases and improving shrimp health through their potential to control pathogens, to stimulate the immune response, to improve water quality and to enhance nutrition through the production of digestive enzymes (Verschuere et al., 2000; Gullian et al., 2004; Wang, 2007). To achieve health benefits, probiotic bacteria must be viable and available at high concentration, typically 106–107 CFU/g of product (Kosin and Rakshit, 2006). Furthermore, incorporation into feed pellets is more effective in conveying probiotics into animals compared to direct application into rearing systems. It is also applicable for intensive aquaculture and requires no additional labor or shrimp handling (Gómez et al., 2007). The viability and stability of probiotics have been a technological challenge in feed manufacturing because probiotics, including Lactobacillus, Bacillus and yeast, are susceptible to the high temperature of the pelleting and drying process. According to Biourge et al. (1998), Bacillus CIP5832 spores in dog diet were found to have in excess of 99% loss after the extrusion, expansion and drying processes. Furthermore, the viable count of yeast in shrimp feed pellet decreased by 105 fold after extruding through a meat grinder at 72 °C for 31 s followed by drying at 65 °C for 6 h (Aguirre-Guzmán et al., 2002).
Fluidized bed drying is extensively used for drying wet particulate and granular materials. In a fluidized bed dryer, the probiotic cell suspension is mixed with a vibrating bed of absorbers or matrix molecules which helps to form capsules by adherence (Nag and Das, 2013). This process is comparatively economical. It involves low energy consumption, high throughput and imparts moderate heat stress to the bacterial cells (Beker and Rapoport, 1987; Nag and Das, 2013). Furthermore, this process was successfully used for the preparation of dried granules or powders containing lactic melatonin receptor agonist bacteria (Santivarangkna et al., 2007; Nag and Das, 2013). According to Nag and Das (2013), fluidized bed drying was able to retain viability of Lactobacillus casei CRL 431 of more than 7.7 log CFU/g during storage at 25 °C for 12 wk. Mille et al. (2004) revealed that the Lactobacillus plantarum viability in casein powder was up to 80% after fluidized bed drying at 35 °C for 30 min. Correspondingly, the survival of Lactobacillus brevis in fish feed was 99% (108–109 CFU/g) after fluidized bed drying at 40 °C for 40–60 min with a moisture content of 5% (Toledo et al., 2010). Several studies have reported that the viability of lactic acid bacteria during drying and storage was enhanced by the addition of protective agents such as trehalose, skim milk, whey protein, soy protein isolate, monosodium glutamate, sucrose, lactose, sorbitol and polymers such as carboxymethyl cellulose, dextran and acacia gum (Morgan et al., 2006; Santivarangkna et al., 2007; Golowczyc et al., 2011; Lapsiri et al., 2013). In the present study, an overnight culture of Lactobacillus lactis 1464 was incorporated into shrimp feed pellets prior to the pelleting process at ambient temperature and dried in a fluidized bed dryer to achieve a moisture content lower than 11%. The effect of the drying temperature, culture pH and protectants on the strain survival during drying was determined. Additionally, the storage stability of the strain in the pellets at 4 °C and 30 °C was also evaluated.
Materials and methods
Results and discussion
Conflict of interest
Dendrobium is one of the largest genera of Orchidaceae, with over 1000 species worldwide (Leitch et al., 2009). Many Dendrobium orchids are important horticultural crops and have been used in commercial trade due to their popular flowering abundance, wide range of flower colors, sizes, shapes, year-round availability and lengthy post-harvest life (Hossain, 2011). Most Dendrobium species are suspected of becoming extinct. Of these, Dendrobium friedericksianum Rchb.f. is a native epiphytic orchid found in tropical rain forests in Eastern Thailand according to the checklist of international species, (Convention on International Trade in Endangered Species of Wild Fauna and Flora, 2014). Due to their beautiful, bright golden-yellow flowers with diameters around 4–5 cm each, the orchid has attracted collectors and so specimens are in high demand for illegal trading. Consequently, this species is on the verge of being seriously endangered in the wild.