Manufacturing of active packaging with controlled release of biocompounds into food is a challenge for the food industry. The incorporation of thermosensitive nanohydrogels in this type of packaging can modulate the delivery mechanism of bioactive agents. The thermosensitive nanohydrogels phase transition was studied in this work. Nanohydrogels were obtained by covering metal nanoparticles of magnetite (Fe3O4) with a polymeric layer of pNIPAM. Phase transition of nanohydrogels was observed by the change of hydrodynamic diameter in a temperature range below and above the lower critical solution temperature (LCST) of pNIPAM (T = 32 ° C). Infrared analysis, hydrodynamic diameter, and thermal analysis were performed in this study. The results demonstrated that nanohydrogels have a phase transition at a temperature very close to LCST of pNIPAM. Also, the nanohydrogels can be an option of nanofiller for manufacturing of active packages responding to external stimuli such as a temperature increase.

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Effects of pasteurization temperature and curd cutting size on viscoelasticity of costeño cheese were evaluated. A 3 2 -factorial experiment was developed in a completely random design (pasteurization temperature: 63ºC / 30min, 73ºC / 15s and 83ºC / 1s; curd cutting: 1, 3 and 5 cm). Pressure required to maintain a constant deformation was determined from relaxation tests by using an EZ Text Shimadzu® texturometer and a 2.04 Rheometer® software. Obtained data was represented by means of Peleg's standard and linear model. Results showed that interaction among temperature and cutting factors significantly affected residual asymptotic modulus "Ea.", resulting in a totally different cutting tendency for each temperature and time ratio level. Pressure decline level "a" and velocity at which pressure relaxes "b" were only affected by main effects of pasteurization, temperature and curd cutting size. When using pasteurization levels of 63ºC / 30min and 73ºC / 15s with curd cutting sizes of 2.8cm and 2.6cm respectively, an increase in the influence of the viscous component is produced in costeño cheese. The opposite occurs when using an 83ºC / 1s pasteurization level, since there is a decrease of this component; prevailing before the elastic component, though. Finally, it was possible to establish that for the 83ºC / 1s heat treatment level, curd cutting size did not affect viscoelasticity of costeño cheese.