Physicochemical, Microstructural, and Microbiological Properties of Skipjack Tuna (Katsuwonus pelamis) After High-Pressure Processing.

Properties of skipjack tuna loins subjected to high-pressure processing (HPP) at 150 to 600 MPa for 1 to 5 min were compared with those of loin that underwent steam cooking for 10 min. Protein denaturation in HPP-treated loins increased with increasing pressure level, but these loins retained between 1.1% and 2.4% more water than steam-cooked loin. Water holding capacity decreased from 57% to 44% when the loins were treated at 600 MPa. ΔE value of HPP loins was between 5.8 and 26.3 when treated at 150 to 600 MPa, whereas it was 34.1 for steam-cooked sample. Hardness of HPP loins increased from 648 to 1,019, 1,918, 5,249, and 4,092 g and springiness changed from 85.2% to 79.7%, 78.2%, 91.7%, and 90.7%, respectively, when treated at 150, 300, 450, and 600 MPa. Protein fibers of HPP loins had a more irregular shape than those of steam-treated loin. Histamine levels of HPP-treated loins were in the range of 3.08 to 3.35 µg/g, identical to that of steam-treated loin. Thiobarbituric acid assay demonstrated that the level of lipid oxidation increment in HPP-treated loins was twice as high as that in steam-cooked one. Undesirable volatile compound contents in tuna loins decreased with increasing degree of protein denaturation. Steam cooking and HPP at 150, 300, 450, and 600 MPa decreased the total aerobic counts by 4.75, 0.12, 1.20, 4.69, and 6.08 log CFU/g, respectively. These results suggest that HPP at 450 MPa and above has the potential to be used as an alternative to the tuna precooking process. PRACTICAL APPLICATION: Information presented here can serve as a guideline for the selection of appropriate conditions for HPP of tuna loins. Our results show that HPP has a potential to replace the highly energy-intensive steam precooking step, which is traditionally required in a canned tuna production process.

Effects of crosslinking temperature and time on microstructure and stability of cassava starch microspheres.

Starch microspheres (SMs) were prepared by a water-in-water emulsion-crosslinking technique at 4 °C and 30 °C for 1, 6, 12 and 24h; the SMs obtained were analyzed for crosslinking density, morphology, crystalline structure, and stability against temperature, pH, and α-amylase hydrolysis. The crosslinking degree at 30 °C was considerably higher than that at 4 °C. SMs prepared at 4 °C for less than 12h incubation had larger size and more porous structure as compared with those prepared at 30 °C, but the morphology became comparable (spherical shape with smooth surface and dense structure) after 24h incubation. All SMs samples displayed amorphous structure. Stability tests revealed that the SMs were very stable under acidic and mild basic pH; however, stability against α-amylase hydrolysis varied depending on incubation temperature and time.

Pasting properties of heat-moisture treated canna starches using different plasticizers during treatment.

Different plasticizers (propanol, propylene glycol, glycerol, erythritol, xylitol and sorbitol) were used for plasticizing canna starch during heat-moisture treatment (HMT). Pasting properties of the modified starches were determined and compared with those of native starch and of HMT starch using water as a plasticizer. Canna starch was soaked in 5% (w/w) plasticizer solutions and adjusted to 25% moisture content before heating at 100 °C for 1h. The least change in paste viscosity was found when water was used as a plasticizer. Viscosity of the modified starches decreased as the molecular weight of plasticizers decreased. Plasticizer content in starch granules increased with decreasing molecular weight of the plasticizer, as well as with increased soaking time (from 10 min to 4 and 24h). However, pasting profiles of HMT starches prepared by soaking for 4h were comparable to those soaked for 24h, indicating that there was an effective limit of plasticizers. The plasticizer content in starch granules played a greater role in HMT than the number of hydroxyl groups.

Nano-structure of heat-moisture treated waxy and normal starches.

Surface regions of untreated and heat-moisture treated (HMT) normal rice, waxy rice, normal corn, waxy corn, normal potato, and waxy potato starch granules were examined by atomic force microscopy (AFM). AFM images revealed surface roughness of untreated starch granules and protrusions with a diameter of approximately 15-90 nm. After treatment, the smooth surface region on starch granules was observed, especially in normal rice, waxy rice, and normal corn starches. A significant reduction in the size of protrusions on the surface of HMT potato starch granules was also detected. The newly formed structures may act as barriers and retard water penetration into starch granules. The blocklet model of starch granule architecture was also confirmed by the AFM images.