Foodborne illnesses are a growing concern for the food industry and consumers, with millions of cases reported every year. Consequently, there is a critical need to develop rapid, sensitive, and inexpensive techniques for pathogen detection in order to mitigate this problem. However, current pathogen detection strategies mainly include time-consuming laboratory methods and highly trained personnel. Electrochemical in-field biosensors offer a rapid, low-cost alternative to laboratory techniques, but the electrodes used in these biosensors require expensive nanomaterials to increase their sensitivity, such as noble metals (e.g., platinum, gold) or carbon nanomaterials (e.g., carbon nanotubes, or graphene). Herein, we report the fabrication of a highly sensitive and label-free laser-induced graphene (LIG) electrode that is subsequently functionalized with antibodies to electrochemically quantify the foodborne pathogen Salmonella enterica serovar Typhimurium. The LIG electrodes were produced by laser induction on polyimide film in ambient conditions, and hence circumvent the need for hightemperature, vacuum environment, and metal seed catalysts commonly associated with graphene-based electrodes fabricated via chemical vapor deposition processes. After functionalization with Salmonella-antibodies, the LIG biosensors were able to detect live Salmonella in chicken broth across a wide linear range (25 to 10 5 CFU mL -1 ) and with a low detection limit (13 ± 7 CFU mL -1 ; n = 3, mean ± standard deviation). These results were acquired with an average response time of 22 minutes without the need for sample preconcentration or redox labeling techniques. Moreover, these LIG immunosensors displayed high selectivity as demonstrated by non-significant response to other bacteria strains. These results demonstrate how LIG-based electrodes can be used for electrochemical immunosensing in general and, more specifically, could be used as a viable option for rapid, low-cost pathogen detection in food processing facilities before contaminated foods reach the consumer.

Naringin, a bitter compound in citrus, may be converted to a nonbitter form by enzymic hydrolysis. Our objective was to determine the feasibility of immobilizing naringinase in a food contact approved packaging film. Naringinase from Penicillium sp. was immobilized in cellulose acetate films with up to 23% efficiency at 7°C. Kinetic studies showed that the free enzyme had an optimum pH=3.5 and the immobilized enzyme pH=4.0. Activation energy decreased upon immobilization (from 14.2 to 11.0 Kcal/mol), thus providing an increased catalytic efficiency for immobilized naringinase. The Michaelis constant for immobilized naringinase (K m =2.1 mM) was lower than for free enzyme (K m =3.6 mM). Keeping films under dry storage for 1 mo at room temperature did not cause decreased enzyme activity. A film area/volume ratio (cm 2 /mL of 10° Brix grapefruit juice) of 7.2 hydrolyzed 60% of the naringin in 15 days at 7°C.

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ResumoEste trabalho teve como objetivo elucidar, por meio da pirólise analítica acoplada à cromatografia gasosa e espectrometria de massa, alterações na composição química da lignina nas bainhas de plantas de arroz das cultivares BR-Irga 409 e Labelle supridas ou não com silício (Si) e infectadas por Rhizoctonia solani. A concentração de Si nas bainhas das plantas supridas com esse elemento foi significativamente maior (2,7 dag kg -1 ) em comparação com as plantas não supridas (0,45 dag kg -1 ). Na presença de Si, a área abaixo da curva do progresso da queima das bainhas foi significativamente reduzida em 19 e 25%, respectivamente, para as plantas das cultivares BR-Irga-409 e Labelle em relação à ausência desse elemento na solução nutritiva. Com base nos espectros de massas obtidos, foram identificados 33 compostos, dos quais 10 foram produtos da degradação de carboidratos e 23 derivados da lignina. Dentre os derivados da lignina, oito compostos eram do tipo p-hidroxifenila, 11 compostos do tipo guaiacila e quatro compostos do tipo siringila. Nas bainhas das plantas das duas cultivares de arroz, supridas ou não com Si, a concentração de lignina (p-hidroxifenila, siringila (S) e guaiacila (G)) foi de, aproximadamente, 15%. Houve aumento na relação S/G apenas nas bainhas das plantas da cultivar BR-Irga 409 supridas com Si e infectadas por R. solani. A maior concentração de Si nas bainhas das plantas de arroz das duas cultivares, que por sua vez resultou em aumento na relação S/G, contribuiu para reduzir os sintomas da queima das bainhas.Palavras-chave: queima das bainhas, lignina, metabólitos secundários, resistência. Silicon altering compounds derived from the pyrolyses of leaf sheaths of rice plants infected with Rhizoctonia solani AbstractThis study elucidated, through analytical pyrolysis coupled to gas chromatography and mass spectrometry, changes in the chemical composition of lignin on leaf sheaths of rice plants of cultivars BR-Irga 409 and Labelle supplied or non-supplied with silicon (Si) and infected with Rhizoctonia solani. The Si concentration on leaf sheaths of plants supplied with this element was significatively higher (2.7 dag kg ). In the presence of Si, the area under leaf sheath blight progress curve was significantly reduced by 19 and 25% for plants from cultivars BR-Irga 409 and Labelle, respectively, in comparison to the absence of Si. Based on the mass spectra obtained, 33 compounds were identified, 10 of which were products from the degradation of carbohydrates and 23 derivate from lignin. From lignin derivatives, eight compounds were p-hydroxiphenil type, eleven compounds were guaiacyl type and four compounds were syringyl type. On leaf sheaths of both cultivars, the concentration of lignin (p-hydroxiphenil, syringyl (S) and guaiacyl (G)) was around 15%, regardless of Si. There was no increase in the S/G ratio only for the leaf sheaths of BR-Irga 409 supplied with Si and infected with R. solani. High Si concentration on leaf sheaths of both cultivars, which in turn resulted in an increase...

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