Preparation and application of bilayer films from raw or cooked purple sweet potato for monitoring minced pork freshness

doi:10.19491/j.issn.1001-9278.2025.09.008

Abstract

Abstract:

In this study， a type of bilayer film was fabricated for monitoring minced pork freshness using raw or cooked purple sweet potato powders as the base material， combined with sodium alginate， titanium dioxide， and citric acid， through a layer⁃by⁃layer self⁃assembly technique. Eight distinct film formulations were comprehensively characterized for their structural， optical， mechanical， antioxidant， and ammonia⁃responsive properties， including X⁃ray diffraction， scanning electron microscopy， water vapor permeability， and controlled release performance. Among these， the STNPR film demonstrated optimal overall performance， exhibiting an opacity of 7.18 mm⁻¹， tensile strength of 2.93 MPa， elongation at break of 39.2 %， moisture content of 26.78 %， water vapor permeability of 0.000 3 g/（mm·d）， water solubility of 50.97 %， swelling ratio of 362.99 %， and DPPH radical scavenging activity of 56.79 %. When applied to monitor minced pork freshness， the STNPR film displayed a visible color transition from eggplant purple to dark eggplant purple and finally to blue⁃black， correlating with pork quality degradation. This colorimetric response provides a simple， reliable， and visually intuitive method for real⁃time freshness assessment， offering practical utility for consumers.

Key words: purple sweet potato, titanium dioxide, bilayer film, freshness

CLC Number:

TQ320.72⁺1

XIE Wei, DENG Zhonghui, YAN Yu. Preparation and application of bilayer films from raw or cooked purple sweet potato for monitoring minced pork freshness[J]. China Plastics, 2025, 39(9): 49-57.

Figures/Tables 14

Fig.1. XRD of different films

Fig.2. The morphology of the samples

Fig.3. The color of bilayer film

双层膜	颜色参数				膜厚
双层膜	L^*	a^*	b^*	∆E	膜厚
SPR	30.12	20.02	3.65	71.76	0.24
SNPR	33.7	29.16	7.25	70.97	0.26
STPR	32.4	21.70	4.81	69.91	0.23
STNPR	32.9	25.75	5.87	70.55	0.27
shuPR	56.52	14.32	24.47	45.06	0.22
shuNPR	71.19	24.77	4.21	35.60	0.35
shuTPR	44.06	31.94	11.82	62.62	0.27
shuTNPR	60.53	12.82	24.43	40.82	0.31

Tab.1. Color parameters and thickness of bilayer films

Fig.4. Opacity of bilayer films

Fig.5. Mechanical properties of bilayer films

Fig.6. Water resistance of bilayer films

Fig.7. Water resistance of bilayer films

Fig.8. DPPH radical scavenging rate of bilayer films

样品	0 min	5 min	10 min	15 min	20 min	25 min	30 min
SPR膜
SNPR膜
STPR膜
STNPR膜
shuPR膜
shuNPR膜
shuTPR膜
shuTNPR膜

Tab.2. Color changes of bilayer films in response to ammonia solution

Fig.9. ∆E of bilayer films in response to ammonia solution

Fig.10. Sustained release effect of bilayer films in distilled water food simulant

Fig.11. Sustained release effect of bilayer films in 50 % ethanol food simulant

时间/h	0	12	24	36	48
膜的∆E	70.55	10.78	14.19	15.89	23.94
膜颜色
pH	6.15	6.68	6.92	7.18	7.42

Tab.3. Monitoring of minced pork using STNPR film at 25 ℃

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