Mechanical properties of maize kernel horny endosperm, floury endosperm and germ

Figures & data

Figure 1. Puncture test system and a typical force-deformation curve obtained from the puncture test

Table 1. List of abbreviations and symbols

Symbols or abbreviations	Description	Calculation
Mechanical parameters
Frp (N)	Rupture force (force at the rupture point)	Shown in Figure 1b.
Drp (mm)	Rupture deformation (Deformation at the rupture point)
Trp (mJ)	Toughness (energy absorbed before the rupture point)
Fby (N)	Bioyeiled force (force at the bioyeiled point)
Dby (mm)	Bioyeiled deformation (deformation at the bioyeiled point)
Finf (N/mm)	Initial firmness (measured at the deformation of 0.015mm)	$F_{inf}=\frac{\mathrm{\Delta }F}{\mathrm{\Delta }D}$
Favf (N/mm)	Average firmness (measured at the rupture point)	$F_{avf}=\frac{\mathrm{\Delta }{F}_{rp}}{\mathrm{\Delta }{D}_{rp}}$
Fp (N)	Penetration force (the average of measured forces at every 1 mm depth up to 1.25 mm depth after the rupture point)	$F_p=\frac{1}{n}{\sum }_{i=1}^{i=n}{F}_k$
AME (MPa)	Apparent modulus of elastic	$AME=\frac{F}{Dd}$
E (MPa)	Modulus of elastic	$E=\frac{AME}{1-{\mu }^2}$
σs (MPa)	Bioyieled strength	$\left|{\sigma }_s\right|=\frac{4F_{by}}{\pi d^2}$
σb (MPa)	Ultimate strength	$\left|{\sigma }_b\right|=\frac{4F_{rp}}{\pi d^2}$

Figure 2. Puncture test results of horny endosperm, floury endosperm and germ in Zhengdan958, Dafeng30 and Jinyu818 at the moisture content of 17.64%. Error bar indicates the standard deviation. Values with different letters in each parameter are significantly different according to the Duncan multiple range test at α = 0.05. Values of p smaller than 0.05 indicate a significant difference at the 95% confidence level

Table 2. P values for the modulus of elastic (E) of maize kernel tissues from different varieties

	Dafeng30-FP	Jinyu818-FP	Zhengdan958-FP	Dafeng30-HP	Jinyu818-HP	Zhengdan958-HP	Dafeng30-G	Jinyu818-G	Zhengdan958-G
Dafeng30-FP	1	0.0396*	0.1751 NS	1.95648e-008**	7.4447e-008**	3.843e-016**	1.14646e-005**	8.67657e-006**	2.59229e-005**
Jinyu818-FP		1	0.1264 NS	1.01426e-007**	3.38769e-007**	4.87635e-017**	2.08316e-022**	1.45078e-022**	2.11326e-022**
Zhengdan958-FP			1	2.3306e-008**	1.46926e-007**	6.76135e-018**	2.88806e-022**	1.95345e-022**	2.37159e-022**
Dafeng30-HP				1	0.0572 NS	0.0439 NS	3.99456e-013**	3.49963e-013**	5.90355e-013**
Jinyu818-HP					1	0.4542 NS	2.34106e-010**	2.15534e-010**	3.02187e-010**
Zhengdan958-HP						1	1.93791e-023**	1.70207e-023**	2.65735e-023**
Dafeng30-G							1	0.6413 NS	0.0555 NS
Jinyu818-G								1	0.0156*
Zhengdan958-G									1

Symbols and abbreviations: FP (floury endosperm), HP (horny endosperm) and G (germ).

NS is non-significant.

* is significant at the 0.05 level (1-tailed).

** is significant at the 0.01 level (2-tailed).

Figure 3. Effects of the moisture content on the mechanical parameters of Zhengdan958 maize kernel. HE, SE and G are the horny endosperm, floury endosperm and germ respectively. Error bar indicates the standard deviation. Values with different letters in each parameter are significantly different according to the Duncan multiple range test at α = 0.05

Table 3. Pearson’s correlation coefficients (r) among the mechanical properties of maize kernel tissues obtained from the puncture tests

	Frp	Drp	σb	Trp	Finf	Favf	E	AME	Fby	Dby	σs	Fp
Frp	1	−0.2821**	0.978 **	0.7267**	0.6491**	0.8243**	0.793**	0.793**	0.9116**	−0.3416**	0.9049**	0.782**
Drp		1	−0.2532**	−0.0275	−0.3934**	−0.4653**	−0.393**	−0.393**	−0.285**	0.5812**	−0.2842**	−0.178**
σb			1	0.765**	0.6483**	0.8268**	0.79**	0.79**	0.9243**	−0.3361**	0.9175**	0.7885**
Trp				1	0.4839**	0.5459**	0.5978**	0.5978**	0.752**	−0.1697**	0.7562**	0.7131**
Finf					1	0.7848**	0.7904**	0.7904**	0.6494**	−0.5031**	0.6489**	0.5096**
Favf						1	0.8604	0.8604**	0.8362**	−0.5134**	0.8395**	0.6776**
E							1	0.9237**	0.8059**	−0.4863**	0.7998**	0.6251**
AME								1	0.8059**	−0.4863**	0.7997**	0.6251**
Fby									1	−0.3407**	0.9902**	0.6514**
Dby										1	−0.3417**	−0.2664**
σs											1	0.7545**
Fp												1

The mechanical parameters are F_rp (rupture force), D_rp (rupture deformation), σ_b (ultimate strength), T_rp (toughness), F_inf (initial firmness), F_avf (average firmness), E (modulus of elastic), AME (apparent modulus of elastic), F_by (bioyeiled force), D_by (bioyeiled deformation), σ_s (bioyieled strength), F_p (penetration force).

* Correlation is significant at the 0.05 level (2-tailed).

** Correlation is significant at the 0.01 level (2-tailed).

Figure 4. SEM micrographs of maize kernel horny endosperm, floury endosperm and germ (x1200). (a) The micrograph of horny endosperm; (b) the micrograph of floury endosperm; (c) the micrograph of germ

Figure 5. Micrographs of the cracks in endosperms when the kernels were subjected to an external force (x1200): (a) horny endosperm, (b) floury endosperm