Spectral Indices for Non-destructive Determination of Lettuce Pigments
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Spectral Indices for Non-destructive Determination of Lettuce Pigments Daniela de Carvalho Lopes 1 & Lorena de Oliveira Moura 1 & Antonio José Steidle Neto 1 & Leila de Castro Louback Ferraz 1 & Lanamar de Almeida Carlos 1 & Luma Moreira Martins 1
Received: 18 October 2016 / Accepted: 14 February 2017 # Springer Science+Business Media New York 2017
Abstract Lettuce pigments play important physiological functions, such as photosynthetic processes and light stress defense. Spectral indices are widely used for predicting vegetable pigments in a non-destructive way. This work was carried out to propose and validate mathematical models based on spectral indices, capable of predicting carotenoid and anthocyanin contents in different lettuce cultivars, grown under organic, hydroponic and alternative farming systems. Standardized Difference Vegetation Index, Simple Ratio Index, and Difference Spectral Index were modified and combined with linear, exponential, power, and logarithm regressions during the modeling process. The most accurate models presented d and r values greater than 0.7 and 0.6 for the external validation, respectively. When estimating carotenoid and anthocyanin contents, the root-mean-square error did not exceed 0.14 and 0.41 mg kg−1, respectively. The maximum mean bias error values were −0.07 mg kg−1 for carotenoids and 0.08 mg kg−1for the anthocyanins. Models based on the Difference Spectral Index with exponential fitting performed better, but linear fittings combined to the other spectral indices also confirmed the feasibility of using the proposed models for estimating lettuce pigment contents.
Keywords Carotenoids . Anthocyanins . Spectrometry . Lactuca sativa L
* Daniela de Carvalho Lopes [email protected]
1
Federal University of São João del-Rei, CSL, MG 424 - km 47, Sete Lagoas, Minas Gerais 35701-970, Brazil
Introduction Lettuce (Lactuca sativa L.) is one of the most grown and consumed salad vegetables in the world, with production of 24,896,115.89 t in 2013 (Faostat 2013) and average daily consumption of 22.5 g/person in Europe (Pérez-López et al. 2015). Lettuce is a rich font of vitamins (A, B1, B2, C, E), bioactive composites, and minerals as iron and calcium. Additionally, it contains high amount of water in its tissues, as well as reduced lipid and energetic contents (Nicolle et al. 2004). Carotenoids and anthocyanins are important pigments found in lettuce cultivars, which perform essential physiological functions in plants such as the photosynthetic processes and light stress defense (Gross 1991). Carotenoids are pigments that protect the chlorophyll molecule from photooxidation under excessive light (Rodriguez-Amaya 2001), also having antioxidant action and presenting provitamin A activity (Rodriguez-Amaya et al. 2008). Anthocyanins are pigments produced by the plant secondary metabolism, playing an important role in the human healthy due to their antioxidant activity (Chon et al. 2012). Chemical analysis of food is increasingly sophisticated, searching for more accurate quan
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